Every July for the past thirty years, up to ten thousand people have gathered at the city of Laguna Niguel, CA to expose their rears at passing trains. Some people have even traveled as far as Europe to take part in this unusual annual event.

The event, which is titled "Mooning Amtrak," can last all day and night with nighttime mooners urged to bring a torch so that passing trains can see their behinds.

Bottom-baring dates back almost two thousand years but this odd ritual is said to have originated from a bar room bet in 1979 at the nearby Mugs Away Saloon when a man who was drinking at the Saloon said he would buy anyone a beer who would flash their rear at a passing train.