Hidden Mouth Cave is a surprisingly large and fun lava cave out on the high desert near Moore, Idaho, in the volcanic country of the Lost River Valley. True to its name, the entrance is tucked away and easy to miss, but inside it opens into a spacious system of three distinct chambers — a genuinely rewarding find for cavers willing to seek it out, and a favorite of local explorers and geocachers.

The cave is a lava tube, formed when the surface of an ancient lava flow hardened while the molten rock beneath drained away, leaving a hollow passage behind. Exploring the three chambers is the main event, and there's a fun twist at the far end: a “secret” back exit for those who don't mind clambering up a precariously balanced log to reach it. It adds a little adventure to the trip, though it's optional — you can simply return the way you came.

Getting there is part of the fun. The cave sits up a hillside reached by a rough backcountry track: you can drive a quad or four-wheeler about halfway up, after which it's roughly a quarter-mile hike that gets fairly steep, with the trail leading directly to the cave. A high-clearance or off-road vehicle is a big help on the approach, and the final walk is a short but real climb.

The cave sits in one of Idaho's great volcanic landscapes. The Lost River Valley and the plains around Moore and Arco are riddled with lava flows, tubes, and cinder cones — the same country that holds Craters of the Moon not far to the south — so Hidden Mouth pairs naturally with a bigger day of exploring the area's volcanic features. Because the GPS coordinates for the entrance aren't widely published and the mouth really is hidden, it helps to go with someone who's been before, or to do your homework on the location first.

Come prepared with the caving basics. Bring at least two light sources per person — the cave is completely dark — wear sturdy, closed-toe shoes and a helmet for the rocky, uneven floor and the log climb, and pack a layer, since lava caves stay cool year-round no matter how hot the desert above. As always, don't cave alone, and let someone know where you're going, since this is remote country with little cell service.

Tread lightly out here: pack out everything you bring, avoid disturbing any wildlife using the cave, and leave the chambers as you found them. For those who love a bit of a treasure hunt, Hidden Mouth Cave delivers — a hidden entrance, three roomy chambers, and a sneaky log-climb exit, all in the wide-open volcanic desert of central Idaho.