In the depths of Hell.

yes, I understand. When I was close, I immediately went there. So, I gathered about 44% of the information, and there are 2 demon cities left. Among the active (uncompleted) quests, I need to find 3 angel units, capture all buildings, and find the Boots of Swiftness. The army is decent. The hero is level 34.

Added 1 minute ago
Okay, there was a castle to the southeast, but it's a dead end. I'll go look for places I haven't been to yet.