Deepest underground structures in the world.
Fullsize image: https://s3-us-west-1.amazonaws.com/h...s_fullsize.jpg
https://s3-us-west-1.amazonaws.com/h...structures.jpg
Previously:
https://www.homemadetools.net/forum/...372#post181457
https://www.homemadetools.net/forum/...825#post186728
https://www.homemadetools.net/forum/...408#post177447
https://www.homemadetools.net/forum/...900#post133596
https://www.homemadetools.net/forum/...630#post162973