Today's Bing.com home page leads to this nice collection of 15 underground tours you can take around the world. Fun stuff.
http://www.bing.com/travel/content/search?q=Underground+Attractions%3a+Cu+Chi+Tunnels%2c+Vietnam&FORM=TRREST <http://www.bing.com/travel/content/search?q=Underground+Attractions%3a+Cu+Chi+Tunnels%2c+Vietnam&FORM=TRREST> Dale
