World Championship in Heroes of Might and Magic III.

In my opinion, the Tower and the Swamp are quite challenging castles in 8mm. It's very likely that you'll get stuck on difficult map sections, and there are other drawbacks as well. It's better to choose something like a Dungeon-Rampart combination. Or rely on getting lucky with the map generation. For example, hoping that the game will give you flight and teleportation, cheap lairs for Naga-Giants, and other similar advantages.