Cursed City

I defeated the hero near the garrison, then went to the human castle, captured the mines, and moved to my own castle. After that, I couldn't go back there.

Ah, I understand. There's a function, either "end" or "finish," I'm not sure which, but that's what the map editor is for. After defeating the guard (the knight standing in front of the garrison), you can't return to the castle; you have to go straight to the second battle with Elaine, so it's better to check her army beforehand, otherwise, you might not be able to win both battles.