Minecraft wiki entry for Elevators, associated text: At the bottom leave a two-block high opening (from the floor) for the entrance. Start placing signs on the opposite wall of the shaft starting with the second block from the ground. Above it place a water source, then jump up into the water and swim upward. Place signs and water sources alternating until you reach the top. The swimming action you need to use to keep on top of the uppermost water block causes you to bob up and down, but some practice makes it easy to work this way.