In the lower part of Skull Castle in the dirt part where there is a whole bunch of crates I moved all the crated and found a button behind them. I hit it but I cant figure out what happened. Can someone plz Tell me.

It opened a previously closed door.

Is that near the lava area? If yes - then it will semi prevent the grating from sinking into the lava when you try to get the chest in that area.

Or it might be opening the door to a vault nearby.

Wyv