Mallory Cave is a historic and scenic hiking destination in the Flatirons above Boulder, Colorado, set high on the slopes of Dinosaur Mountain within the city's Open Space and Mountain Parks. First explored by a University of Colorado student in 1932, the cave and the rugged trail that climbs to it have been a beloved Boulder adventure for generations — a rewarding scramble through classic Front Range terrain with big views along the way.

One crucial thing to know: you can no longer go inside the cave. Mallory Cave is home to a colony of sensitive Townsend's big-eared bats, and to protect them from white-nose syndrome — a devastating disease spread in part by humans — the cave entrance was gated in 2011 and is permanently closed to entry. On top of that, the final approach to the cave is closed seasonally from April 1 to October 1 each year to protect the roosting bats, so the upper trail is only open in late fall and winter. Please respect the gate, the signs, and the closures — the bats depend on it.

Even without entering the cave, the hike is well worth it. Starting from the NCAR Trailhead (off Table Mesa Drive at the National Center for Atmospheric Research), the route heads west and climbs through forest and rock, with a short, hands-on scramble near the top, and it connects to Boulder's vast Mesa Trail network if you want to extend your outing.

Plan a fall or winter visit if you want to reach the cave area, wear sturdy shoes for the rocky final pitch, carry water, and leave no trace. A piece of Boulder history wrapped in a great little hike, Mallory Cave is a rewarding trek — just admire the cave from outside, and let the bats be.