Zamek Krzyżacki po angielsku?

Właśnie, jak to będzie...?

the Teutonic Castle

the Castle of the Teutonic Order (...Zakonu Krzyżackiego)

'castle of the teutonic knights'. another qiute common name is: 'crusader castle of the teutonic knights'. a/the before 'castle' depends on the context.

a/the 'castle of the teutonic order' is fine too.