Apparently, the biggest hole on earth is a diamond mine located in Eastern Siberia near the town Mirna. It It is 525 meters deep and 1.25 km. To give you an idea of the scale, here is a picture:
click to enlarge
That is one huge hole! I would describe it as gargantuan. Allegedly, it actually creates a suction well above it making it a no fly zone.
source: prezwho
[tags]hole, biggest hole, russia, diamond mine[/tags]