This is not a really trick or something, but some (strange) feature in Minecraft. Stone slabs are translucent when lit from below. So you can create nice patterns in dark rooms. To my knowledge mobs do not spawn on slabs, so you should be safe to create it without going to risk a flood of mobs.
Step 1: Dig a One Block Hole
Step 2: Place a Torch Inside
Step 3: Cover With Stone Slabs
Step 4: Dim the Light
Once external light sources are dimmed or removed you will see the torches through the stone steps.