entrance to a tunnel. first one we saw today. every sunken meeting room had emergency tunnel exits (in case of bombing from Americans) map of the area
diagram (cut-away) of the tunnels underground. amazing 3 story development. i wouldn't want to become a resident though. the long hole down (with blue at the bottom) is an underground water well, by the way. the boxes under stairs are booby traps (with sharp bamboo pungee sticks) in case "heavy" Americans might try to follow.
most of these tunnels had to be crawled through. there's even places built so narrow, only skinny Vietnamese could fit through. Westerners would get stuck like angry Winnie the Poohs.