Lonely Planet review for Malbork Castle
This is Europe's largest Gothic castle and was once known as Marienburg - headquarters to the Teutonic Knights. It's one of Poland's oldest, and a splendid example of a classic medieval fortress, with multiple defensive walls, a labyrinth of rooms and chambers, and some exquisite architectural detail.
It was constructed by the Knights in 1276 and became the seat of their Grand Master in 1309. Damage sustained in WWII has been repaired since the conflict's end, and it was placed on the Unesco World Heritage List in 1997.