A more cave-like, brownish-reddish, underground Dungeon would be a really useful addition! If you go that direction, you could revise the current Dungeon tileset to be more of a polished above-ground Castle.
Yes, that's what I'm thinking. A brownish/reddish dungeon is more appropriate. And the current dungeon to become as a stronghold/castle tileset.
Now that I have 2 tilesets to do, it should take a bit more time to do it. But I hope to finish it in late June or early July.