Singing carols at Christmas is nothing out of the ordinary, but caroling underground definitely breaks with tradition.

Musicians in central Wisconsin have started a new tradition of performing at one of the state's natural caverns.
   
The holiday concerts known as "Caroling in the Cave" started six years ago when a singing group toured the "Cave of Mounds."

"There was a group of tourists that were traveling that happened to be a singing group. And they noticed the acoustics just from the tour guide talking, myself, and did a little impromptu concert -- one in the back passage ways. And we thought, 'Wow!' Joe Klimczak, general manager of Cave of the Mounds National Natural Landmark, recalled.

"We thought what a great way to have a charity event, give a chance for some local musicians to have a very unusual venue for a concert," he said.

Visitors sang along as candles lit the walls and set the mood.

"It's like, being in this old place, in the old earth while singing these old songs. It was fantastic," audience member Bill Robichaud said.