Malbork is the reportedly largest castle in the world, so searching for a larger one may be futile.
It stands at the confluence of two warring groups: the Germans, specifically the Teutonic Knights, and their opponents, the Baltic peoples.
I can't say much more about the German castles than has been said in another post. But I urge you to look at the other side, the Baltics.
Specifically, the Estonians were the Baltic people most successful in resisting the Teutonic Knights. Probably more so than the Lithuanians and Latvians. For this, and other reasons, the Estonians were better than most other Europeans at building castles. Their capital of Tallinn (formerly Reval) has the most castles per land area of any city in Europe. And some of them are older than Malbork.