Poland has much Lithuanian heritage as Lithuanian and Polish destinies have been intertwinned for centuries. Between 1569 and 1795 Poland-Lithuania was a united Commonwealth and many Lithuanian decisions used to be taken in modern-day Poland. Cracow served as the joint capital and its Wawel castle is a pantheon of Lithuanian monarchs as well as Polish.
Poland still has locations where ethnic Lithuanians are a majority (Punsk/Punskas, Sejny/Seinai area). Those are likely the only foreign places where one can feel as in Lithuania. There are Lithuanian museums, inscriptions, Christian masses and schools. Patriotism likely surpasses that in Lithuania; Columns of Gediminas are used extensively in building decor.
Armies from nations further West have passed or used to base themsleves in Poland when marching against Lithuanians. Northern Poland (Malbork castle) used to serve as a base for Teutonic Knights and the Grunewald (Žalgiris) battle has been fought not that far away. The famous pilots Darius and Girėnas died there as they flew towards Lithuania after crossing the Atlantic ocean (memorial now stands).
Between 1569-1795 Lithuania and Poland were a single country - Polish-Lithuanian commonwealth. The collabortive efforts started much earlier by 1385 Union of Krėva (Krewo) when Jogaila (a Lithuanian) was crowned as king of Poland. Jogaila was a scion of Gediminid dynasty (ruling Lithuania at the time), but as he was the first Gediminid to rule Poland the Poles call the dynasty Jagiellonian after him. Gediminids/Jagiellonians then vied with Habsburgs for prevailing in Eastern Europe. Many dynasty kings are buried in Cracow which was the Polish-Lithuanian capital.
Main pantheon of Cracow is the Wawel Cathedral, part of the royal palace. Jogaila himself rests in a covered red marble grave. Most other leaders are buried in the cellars. Holy Cross chapel has a grave of king Casimir (1440-1491), Sigismunds (Žygimantai) chapel includes graves of Sigismund the Old (1506-1548; Lithuanian: Žygimantas Senasis) and Sigismund Augustus (1548-1572; Lithuanian: Žygimantas Augustas). Maryacka chapel is the final resting place of Stephen Bathory. Vasa chapel has been constructed for the Vasa dynasty of Swedish origin which was elected to rule Poland-Lithuania by its nobles after the Gediminids died out. There are also graves of Jan Sobieski (Lithuanian: Jonas Sobieskis), Michael Karibut Wiszniowecki (Lithuanian: Mykolas Kaributas Vyšnioveckis), Stanislaw Leszczynski (Lithuanian: Stanislovas Leščinskis) and August the Saxonian (Augustas Saksas). Adam Mickiewicz (Adomas Mickevičius) - A poet who wrote in Polish but considered himself Lithuanian because of his Lithuanian origins (something not unusual in the era) - is also buried there, as is the leader of 1794 uprising Tadeusz Kosciuszko (Tadas Kosciuška).
The Wawel grave of Poland-Lithuania's final king Stanislaw August Poniatowski is however empty. After Russia annexed Lithuania and much of Poland by 1795 he lived in exile in Saint Petersburg and was initially buried there. In 1930 the Soviets offered Poles to return the remains but the Polish opinion on "the king under whose rule the country collapsed" was understandably divided. He was thus reinterred in a village near Brest (today's Belarus) rather than Wawel in 1938 and moved to Warsaw's St. John Cathedral after the Poland's communist regime went bust.
Cracow University is named after Jogaila (Jagiello).
Warsaw became the capital of Polish-Lithuanian Commonwealth in 1596. It was transferred there by king Zigmantas Vaza (Zygmunt Vasa) from Cracow. The place had been chosen as a mid-point between Cracow and Vilnius, respective capitals of Poland and Lithuania (in reality Warsaw is 450 km from Vilnius and 300 km from Cracow, this likely representing the larger Polish influence in the Polish-Lithuanian Commonwealth).
Polish-Lithuanian Commonwealth existed for two more centuries, allowing Warsaw to accumulate locations that remind of the Polish union with Lithuania.
Likely the most important among them is the Royal Palace (destroyed during WW2, rebuilt afterwards) which once housed the family of the monarch of "both nations". Polish-Lithuanian monarchs had little influence at the time and the real Power was vested in Seimas (Parliament), which also convened in the same palace (Great Hall). The world's second constitution (1791 05 03) was proclaimed there. Near the Great Hall ceiling there are coats of arms of Poland and Lithuania (Vytis) as well as the coat of arms of all the Voivodships (administrative units), of which three (Samogitia, Vilnius and Trakai) were within the area of modern-day Lithuania. They are represented by the Samogitian bear, Vilnius Voivodship symbols (which includes Vytis), and a plain Vytis representing Trakai (as the Voivodship had no coat of arms, using the Lithuanian one instead). The Palace museum has many historic maps of Lithuania.
In Warsaw St. John's Cathedral the final joint ruler of Poland and Lithuania King Stanislaw August Poniatowski (Lithuanian: Stanislovas Augustas Poniatovskis) is buried. There are also commemorative plaques for Vilnius University and Poles of Lithuania. Moreover, the Cathedral is also the final resting place of Gabriel Narutowicz (Lithuanian: Gabrielius Narutavičius) who was born in Telšiai to a family of somewhat Polonized Lithuanian nobility. They reflected the final division of a "Polish-Lithuanian nation" as Gabriel Narutowicz's own brother Stanislovas Narutavičius became one of twenty signatories of Lithuanian declaration of independence on 1918 02 16. The Polish-Lithuanian relations reached their nadir soon afterwards with the Polish occupation of Vilnius region when entire Eastern Lithuania became ruled from Warsaw once again (1920-1939). References to the era in Warsaw plaques may still evoke controversy among Lithuanians.
Warsaw street names remind of other Polish-Lithuanian era figures. The only difference from similar memorials you may find for them in Lithuania are in names: Poles use Polish versions while Lithuanians use Lithuanian ones. For example, Emilii Plater in Warsaw is the same famous female fighter against Russian domination that is known as Emilija Pliaterytė in Lithuania.
Before World War 2 most of today's northern Poland was ethnically and politically German.
During the 13th-15th centuries pagan Lithuania fought a seeminly eternal war against the German Teutonic Knights who sought to spread Christianity (according to critics, more likely to loot and destroy). Their headquarters was Malbork (Marienburg) castle, today rebuilt for better imagination of knights' lifestyle.
The largest of the battles against the crusading knights took place in Grunewald (known as Tannenberg in Germany, Žalgiris in Lithuania). ~70 000 soldiers participated in this one of the largest medieval battles where a united Lithuanian and Polish force vanquished the Teutonic Knights. The battlefield is now a popular tourist place with medieval souvenirs and a megalomanic monument. The battle has a great importance in Lithuania as many streets and sports franchises are named after it, including the most powerful basketball (Žalgiris Kaunas) and football (Žalgiris Vilnius) teams.
In Soldin forest near Myslibisz a plane "Lituanica" crashed in 1933. Piloted by Steponas Darius and Stasys Girėnas this plane flew succesfully over the Atlantic with destination in Kaunas only several hundred kilometers away. It was the second longest flight time today, first Lithuanian plane to cross the Atlantic and the world's first transatlantic air mail service (the mail did not burn and was symbollicaly flown from the crash site to Lithuania the next day). The pilots became martyrs and even the Nazi Germany permitted construction of the Lithuanian pilots monument (two interlinked crosses) at the crash site in 1936 despite the German claim over Klaipėda region which shattered Lithuanian hopes to particiapte in Berlin olympic games the same year. The monument has original German and Lithuanian plaques. After World War 2 when the lands were added to communist Poland a Polish plaque was installed. Curiously the monument surivived even the iconoclastic communist regime and remained a place of respect. A traditional Lithuanian chapel-post now stands at the place where Steponas Darius body was discovered; a memorial barn is nearby.
The Northeasternmost area of Poland is unique in the world. This is the only area beyond the Lithuanian boundaries where Lithuanians make the majority (~80%). Lituanity is felt here even better than in Lithuania itself: home fences and even a derelict former gas station bear patriotic symbols such as the towers of Gediminas. Many signs are bilingual Polish and Lithuanian. Unlike in Lithuania, in Poland bilingual signs are permitted in minority-majority areas. There has been situations however when vandals damaged the Lithuanian part of the signs but ~2013 most have been rebuilt.
The capital of Poland's Lithuania is Punsk (Punskas, pop. 1200). Its Accension church yard hosts a monument to Lithuanian anti-Soviet partisans. The daily mass is celebrated in Lithuanian and only in Sundays there is a single Polish mass. Church interior is more Polish however, with gold-plaqued statues of saints. Lithuanian museum is nearby. There are two of them in Punsk: Juozas Vaina ethnographic museum and Punsk history museum.
The greatest modern gem of Punskas area is the Prussian-Yotvingian settlement in Ožkiniai village (2 km south of Punsk). Prussians and Yotvingians were Baltic tribes (related to Lithuanians) annihilated by German crusaders; they remained pagan and left few historical descriptions. Nonetheless a local Lithuanian businessman enthusiastically builds up the massive locality since 2001. No one can tell if it looks authentic or not but it certainly feels atmospheric and believavle, with a small castle surounded by a ditch, a village, places for sacred fires, Baltic heroes path of fame. The settlement is well integrated with the local forest and no modern edifices are visible from no locations. One can feel as in the past; both Poles and Lithuanians bring their excursions here and Baltic neo-pagans celebrate their holidays.
A more traditional open-air museum (skansen) is located going from Punsk towards Sejny. It includes a 19th century 5-building farmstead full of museum materials, there is a barn and an inn and all these are outflanked by a modest Žalgiris battle monument. Recent extensions include two "tents of masters" (one for a language master and another one for music master) and improvised ground labyrinth that leads to a written folktale of "Eglė the Queen of Serpents" (in Lithuanian, Polish and Belarusian), an observation point, and some activities. An annual amateur village theater festival takes place here.
Minor places of interest around Punsk are a stone commemorating 1990 Lithuanian independence restoration (in Kampuočiai), a memorial for knygnešys P. Matulevičius (1956, in Kreivėnai), Vytautas the Great memorial (1930, Burbiškiai). There are many stone crosses with Lithuanian inscriptions.
The largest town in area is Sejny (Seinai, pop. 6000). It is an old diocesan centre, anchored on the 1632 Virgin Mary church. The castle-like former priest seminary and monastery stands nearby. Sejny was once a Lithuanian town and the early 19th century creators of the seminary claimed that people in Sejny area "speaks little Polish". During the Lithuanian National Revival Sejny has been an important center of Lituanity where a Lithuanian "Šaltinis" newspaper used to published since 1906. At 1897 a Lithuanian writer Antanas Baranauskas became Sejny bishop (his sculpture has been constructed in 1999 in front of the church under Lithuanian efforts; he is buried under the church). Author of the Lithuanian National Anthem Vincas Kudirka as well as Vincas Mykolaitis-Putinas who later wrote a semi-autobiographical book on priest's celibacy/love dilemma, both studied at the seminary. Out of the 25 students in 1829 21 were ethnic Lithuanians.
The final fate of Seinai (and Punskas) has been decided in years 1919-1920. Both Lithuania and Poland were newly independent and were partitioning the lands of the former Commonwealth. The power in Seinai/Sejny switched many times these years, but the 1920 capture of the town by Polish forces proved to be final (the Poles continued their advance on Vilnius and Eastern Lithuania, and the bitter Polish-Lithuanian territorial dispute continued until World War 2). Berzniki village cemetary is full of the reminiscences of those days. Lithuania has recently built a gravestone with the inscription "To those died for motherland freedom" there for its fallen soldiers of the 1920 battle. Some Poles protested the inscription claiming that these soldiers died when attacking Poland. One opponent was a local priest who initiated construction of a neighboring "Ponary cross" for "Polish civilians killed by Lithuanians in World War 2" (even though the Berzniki cemetary has no graves of such victims). On the other side of the Lithuanian memorial a stone with a list of Polish-conquered cities in 1920 now stands (among them the Lithuanian town of Druskininkai). Furthermore an "alternative" memorial for Lithuanian soldiers was built by the Polish side - a cross beyond the cemetery wall where an inscription declares that Lithuanians helped the Russians to attack Poland. All these events created a diplomatic friction and even caused Poland's Lithuanians to appeal to a Vatican nuncio claiming the priest's actions are against Christian spirit.
The true events of the era were such: "Lithuanian" and "Pole" were a political choice rather than just ethnic categories: many people of Eastern Lithuania spoke Polish better than Lithuanian even though they were of Lithuanian origins (due to a centuries-long linguistic shift). Lithuania considered them to be Lithuanians, Poland considered them Poles (and sometimes even held the entire Lithuanian nation to be a subset of Polish nation). A war started and its results still cause some Poles and Lithuanians to dislike the other nation. This hate came through during the World War 2 when there were both Poles who murdered Lithuanian civilians and Lithuanians who murdered Polish civilians (the Berzniki cross however remembers only the latter). The Polish-Lithuanian war partly overlapped with the Polish-Russian war, that's why Lithuanians are accused of helping Russians (even though Lithuanians and Russians had a different agenda and even fought each other in the same volatile 1918-1922 period).
Currently Sejny is ~17% Lithuanian and there are few Lithuanian inscriptions but the town is still a center of Lithuanian culture. Lithuanian mass is celebrated in the church, a Lithuanian consulate is nearby, there is a Lithuanian "Žiburys" school (2005), cultural center "Lithuanian home" (1999), bi-weekly newspaper "Aušra".
Punsk and Sejny area forms just a small part of Podlaskie (Lithuanian: Palenkė) Voivodship. This territory of 1 200 000 inhabittants with a captal in Bialystok (Lithuanian: Balstogė) was part of the Lithuanian Grand Duchy until the Polish-Lithuanian Union of Lublin (1569). The name "Palenkė" means "[A Lithuanian land] next to Poland". The modern voivodship has been established in 1999 but its coat of arms reminds its history: it is a combination of the Polish eagle and Lithuanian vytis. Vytis is also used in the coats of arms of Bialystok, Bransk, Sedica and other cities/towns; many cities/towns of the area has historical Lithuanian names that are not a simple transliteration of the Polish ones.