If you decide to enter Dungeonland, it's important to either enter with a large unit count or have an anchor (a location which can fortify to one of the 2 corner entrances) so that you can fortify into the Dungeon additional troops. In the latter case, you'll want to make sure not to abandon locations as you progress, to allow fortification to your spots that are attacking monsters. Note, if you kill a monster, leaving 1 or more units on the territory will ensure it does not regenerate.