I bought Dungeon of the Endless a couple of days ago on Steam, and really enjoyed their lighting and tower defence mechanic. Basically in that game you explore levels and you can choose to turn lights on in every room you go through. When you do that, creatures can no longer come from the direction of that room to attack you. It works really well as their central gameplay mechanic, and I thought I'd experiment with something similar in our game.
There have always been a number of lights around the levels, but I had a go of making them all turned off by default. The player can then turn them on as they go past. Firstly this acts as a way of reminding the players where they came from. Secondly, it makes it less likely that a creature will come from that direction to attack them in future.