Everything at the site is camouflaged with leaves, so that even when the U.S. dropped dioxin (
Agent Orange) at 30X the recommended application rate to defoliate the area, the tunnels were nearly impossible to spot.
Even the smoke from cooking fires was vented through numerous small tunnels far from the sites themselves so that it would be nearly unnoticeable
They maintain about 30 meters of the tunnel the way it was so that brave turistas can see what it was like. The darkness is total and you can only crawl on your hands and knees; short as the distance was, I was glad to emerge into daylight!
About a third of American troops were killed in simple pit traps like this one
Here's a mock-up of a door trap that would be triggered if someone pulled the door open -- quite lethal
I would think this would be a hard place to visit for a former U.S. military person who served in this war. For one thing, the jungle has entirely reclaimed it, Agent Orange notwithstanding, so it's as it was during the War. All the museum staff wear Viet Cong uniforms, and there's even an arcade where, for $1 a round, you can fire any of the weapons used during the War.