A dusty tunnel to the side leads to an old dwarven construction facility. Disused parts of golems and other machinery litter the ground. There is surely treasure here, but these tunnels won't lead him to the outside of the mountain!
The DLC introduces a new puzzle element, golem buttons. Push these to cause the golems to move and push things around, freeze in place, or imitate you! This is a level pack for Sub Terra Draconis, providing an extra map with 30 new challenges. The new map is unlocked immediately after the tutorial; you don't have to solve puzzles to find it.
https://store.steampowered.com/app/1344591/Sub_Terra_Draconis__The_Golemworks/