Warning. This page contains *major* spoilers for every dungeon. Use only if you're really lost and try to avoid looking at future maps if you can all avoid it.
Also, these images don't account for the changes made for update 1.1 (there is a secret dungeon connected to the first dungeon that's not in the map below for instance).
Wyvern Mage's Mountain Fortress
The Frozen Ocean
Elegad's Desert Ruins
Temple of the Machine / Water Temple