Before you and Anton was colossal door bridge and walls made of bronze-like material that seemed baffling in scope and how intricate the designs were. All carrying iconography of the Dwarven race.

Dwarven Citadel is a partial abandoned Dwarven Hold that somehow got stuck in the Dungeon of Change. Only few dwarves know how the Citadel suffered it's fate but a dwarf is a very tight-tight-lipped thing.

For those new, here is the start of the Dungeon of Change series: Darkwood

Generally recommended to start there to understand the lore a bit more and the character Anton Goebel.