Ellen Braun admits she was a little nervous when she and bandmate Joe Shea were asked to perform in a cave deep in the heart of Grotto Mountain.

But the singer-songwriters who make up the folk duo Trundled got harnessed up, put on their helmets and went to what's called the Grand Gallery — part of the Rat's Nest Cave near Canmore, Alta., — in October.

"It's a big, giant room in a cave," she said in an interview.

They immediately started a sound check and sang an a cappella version of one of their songs.

"It was so cool how our voices just resonated off the walls," said Braun. "It was a really amazing experience."

The musicians will haul in their guitars on the next trip Dec. 16 for a full acoustic concert — one of four shows which are part of the Spirit in the Mountain concert series at the cave this winter.

Ellen Braun and Joe Shea are part of musical duo Trundled. (Canadian Press/Handout, Ellen Braun, Trundled)

Similar concerts have been taking place for about a decade in an area called the Volcano Room, which is about 100 metres underground inside Tennessee's Cumberland Caverns. They draw fans from around the world who are interested in live music and cave exploration.

Adam Walker, who owns Canmore Cave Tours, said the Grand Gallery concerts started in 2015 when the company was asked by the town of Canmore to get involved in its Christmas festivities.

"We've always known it to be a pretty incredible place to have some music, but we never formally created an event," he said. "In 2015, I said, 'What the heck. Let's give it a go."'

A local community choir performed in the cave for five nights.

Walker said the experiment provided a template for holding other cave concerts, which include a 30-minute hike up to the cave and then a 20-minute journey down about 10 storeys — nearly 50 metres — into the Grand Gallery.

'A really private performance'

"You have to earn it," he said. "It's not for everybody, but it's a really private performance. There are only 24 people plus the musicians inside, so it's really small and intimate."

Walker said they will hand out blankets and cushions for people to sit on as they listen to the hour-long concert.

"The acoustics in the cave are phenomenal."

Braun said she and Shea are looking forward to performing and will even record a few of their songs in the cave.

"I was actually in that cave maybe 15 years ago or more," she said. "I never would have imagined ... that I would be a full-time musician and booking a gig in there.

"Neither of us had ever sung in a cave before."

Other bands involved in the concert series include The Silkstones, an indie-rock group from southern Alberta on Dec. 14; Elk Run and Riot, a Canmore folk-rock band, on Dec. 15; and Seth Anderson, a local folk musician with East Coast roots, on Dec. 17.