This is my concept for a two part map. The surface and the subterranean sections link up through the cave and the mole holes. The idea is to have some vicious gopher or mole like creatures that need to be destroyed. The beasties will of course run when injured, unless they can lure a player down to someplace below where they can be isolate and destroyed. So the players can ultimately accomplish their goal only by learning the layout and herding the mole monsters around to cut off and destroy them. For the sadistic GM (you know who you are) after warren is cleared the players can learn why the devil's gophers wouldn't flock to the surface. When the players exit the warren the dragon (or other suitable monster) that preys on the critters lands. From the one with the hammer to the one playing peek-a-boo with death in the game of whack-a-mole that is the adventuring life.

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From below

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and the surface world

Not sure if the surface isn't a bit washed out looking, but I wanted the feeling of coming from the dimly lit underworld to the blindingly bright surface. Tried a number of fancy borders, but none of them felt well in keeping with an encounter style map. I am a bit iffy on the section where one part of the tunnel goes over the other, but I thought it would be to0 simple if the whole tunnel system was 2D.