One can play the game indefinitely by using two players and resurrecting the dead playing by the player that's still alive. Of course this approach fails if both players die simultaneously.
Also, if you stand still for a few minutes, all walls turn into exits. This is useful sometimes because levels past level 8 are random and not always solvable, especially if teleporters keep sending the player to the wrong place.
Interspersed with normal levels are bonus levels where you have to collect treasure and make it to an exit within 20 seconds.