Minecraft wiki entry for Custom_maps, associated text: Redstone Puzzles. These will give you some redstone components, such as a repeater or two and some redstone dust, and ask you to rewire a door or something to open. Check the relative redstone sections on them in this wiki to find some tips on how to make the most of what you have.
Mazes. Wander around narrow paths aimlessly until you see a door. Mazes can be very fun to play. At each fork, it may help to mark chosen paths with a torch to track where you have been.