Black cube

Directions
See the Debug area page for details on how to reach it. From the Nexus waypoint:
 * 1) Right
 * 2) Right
 * 3) Right
 * Up

In the room with the rotating black square, stand in the center of the square, and jump repeatedly. There should be a sound, just like the one when falling into a pit. After a few dozen jumps, the gates will open. Go Up to claim the cube.