An expedition into “virgin” cave passages found at Carlsbad Caverns National Park in New Mexico has discovered an isolated pool of liquid believed to have never before been seen by humans.

Carlsbad Caverns posted news of the discovery this week on Facebook, calling the site “completely pristine” and speculating bacteria in the water “evolved entirely without human presence.”

A photo shows the pool surrounded by white frosted rock, and filled with an odd-looking liquid that resembles thick lime yogurt.

“This pool has been isolated for hundreds of thousands of years and had never seen light before that day,” said Rodney Horrocks, Chief of Natural and Cultural Resources at Carlsbad Caverns National Park.