The strongest castle in Heroes of Might and Magic IV.

In the Castle, you need to build units that are most effective against your opponent. If your opponent is the Haven faction and has built Mages and Djinns, then if you are playing as Chaos, you absolutely need to build Black Dragons or Magic Dragons. If you are playing as Sylvan, this is just an example. You also need to adapt to the map.
The fact that in Heroes IV there is a choice of creatures that can be recruited in the Castle is a great achievement in the Heroes series. It's a shame that no one appreciated this. But this provides more opportunities in strategy and more variety in the game.