Zamek w Malborku

Originally constructed by Teutonic knights, once the world's biggest brick castle and now a Unesco World Heritage Site. The castle has been expanded several times. Its sheer size is impressive, and historic stories are shared in impressive storytelling. The castle didn't escape bombings during WWII but has been restored. The castle is one of Poland's most famous and best-visited castles. 

(Due to its popularity, keep possible queues for tickets and tours in mind. However, the castle offers several ways to purchase tickets.)