Mammoth Cave is known to be the world’s largest cave system . Now, it’s even longer than we previously thought. Eight miles longer, to be exact, according to the discovery first released by the nonprofit Cave Research Foundation. These previously unknown dark passages bring the believed distance of the caves to 420 miles long.

Mammoth Cave is located at Mammoth Cave National Park in Kentucky, and each year volunteers from the Cave Research Foundation come to the cave to try to discover more unknown passages.

These volunteers went through a complicated process that will lead them trekking in complete darkness in an “abstract subterranean landscape,” only using compasses, measuring tapes, and range finders to reveal these new passages.

“So they most likely will not be included on any new trail routes in the near future anyway. Part of that goes along with preserving a protecting the resource. You know we want to minimize our impact to areas of the cave. We would like to study them and see what the ecosystem is like in those new areas,” said Jennifer Cooper, public information officer, in a statement.

Though these newly discovered passages will not be open to the public, many other passages are open in the five-level cave system for visitors to explore.

The park is open to the public and currently requires face masks to be worn by all visitors. For more information on visiting the cave and Mamaonth National Park you can visit their website.