4 ms·

Not an endorsement but this is cool. 10 tons of concrete http://youtu.be/lFg21x2sj-M http://youtu.be/lFg21x2sj-M

• jacquesm 11y ago
  That's an underground city by any standard.
• DrScump 11y ago
  I saw that on PBS, probably a "Nature" or "Nova" episode.