Cyclopolis is a very large dungeon located behind the mountains north of Edron (here). It was built by the Cyclopes, and reaches several floors below surface.
Many creatures share this city with the Cyclopes, including Elves, Wild Warriors, Minotaur Archers, Dwarf Soldiers, Elf Scouts, Minotaur Mages, Minotaur Guards, an Elf Arcanist, Orc Berserkers and Orc Leaders! Further below the surface you can even find Fire Elementals and the fast and mighty Behemoth. There is a ramp up to the Behemoth Quest on floor 8.
On floor 4 you can see a lot of Giant Swords north-east of the magic forcefields.
Southern room (bottom of the picture):
Floor 6 - top room
And in the rooms outside around: