The Viet Cong inflicted a lot of damage on the US and South Vietnamese forces from these tunnels, and despite committing thousands of troops to find the tunnels, had virtually no luck. The US forces finally bombed out all of the land and collapsed most of the tunnels. The american bombers in destroying the tunnels, supposedly destroyed villages and ecology and more square kilometers of land in the history of warfare.
The other thing that you can do at Cu Chi is fire off a host of weapons. You can choose from an AK 47, M16, M60, and a host of different pistols. I choose to fire 5 shots of an M16 and 5 from an AK, just because I knew I would likely never have that chance again. I also wanted to see the differences in the weapons on the two sides. I also knew a lot of guys in ROTC in college that are now in the military, so wanted to see a little about how if feels to shoot the gun.
The guns are a lot louder, and kick a lot harder than I thought. I found it extremely hard to be accurate with the guns. So when Rambo is holding an M60 in each hand and blowing away Vietcong, it's not too realistic. I guess we already knew that though...
A couple of english guys that are staying at the hotel I was at were pretty funny. They each bought like 100 bullets. One guy changed into a white James-bond-like suit, and fired a bunch of guns, including an M60. The vietnamese guys working there looked absolutely amazed and laughed their asses off.. I don't think they had ever seen anything like it. This crazy blond white guy in a white suit firing off machine guns like a madman.