This contraption uses a glitch (hopefully not the kind that's going to be fixed :P) to teleport a player upwards to the next available space. A fast clock is attached to pistons that mash two blocks together (imagine a trash compactor on speed). When a player enters the mashers, they are teleported to the highest block above the teleporter. Incredibly convenient to have down at bedrock level to quickly get to a safe surface area or tower.