Minecraft wiki entry for Mining, associated text: Descend to the bottom again using the ladder. Be careful, because the center of the shaft is not filled in yet, and it's possible to fall to their death. Once at the bottom, stand in the middle of the shaft and fill it with blocks. Hop upward and place blocks beneath themselves. When they reach the top, leave the central pillar 1 block below the surface (see screenshot). Leaving it 1 block lower allows players to enter the descent shaft simply by walking in.