This dungeon is mostly medium-sized islands surrounded by lava. Mercifully, you begin the level with the ability to build Stone Bridges. Your imps will immediately claim a Portal, so you will have to dig out some space right away and build a Lair and a Hatchery for the Goblins and Fireflies that will start coming in. Also dig out a large space on the island west of your Dungeon Heart to build a Workshop in when it becomes available, but take care to leave some spaces where you will be able to put Doors. If you plan decently, keep digging and claiming land to the west, and make sure to leave yourself access to enough Gold Seams, you should be able to finish this dungeon before you are even able to build a Prison.