Minnetonka Cave is a dazzling underground wonder high in the mountains above Bear Lake near St. Charles, Idaho — the largest developed limestone cave in the state, and one of the highest, with its entrance at around 7,700 feet in the Caribou-Targhee National Forest. A guided tour leads visitors through a cool, beautifully decorated world of stalactites, stalagmites, and ancient fossils that's well worth the trip into the high country.

The cave is experienced on a guided tour run by a Forest Service concessionaire. The route winds about three-quarters of a mile through nine chambers, climbing and descending a total of 888 stairs over roughly 80 minutes, with guides stopping to point out formations and share the cave's geology (and give you a chance to catch your breath). It's a moderately strenuous but family-friendly adventure.

A few things to know before you go. The cave is open seasonally, roughly Memorial Day weekend through Labor Day (depending on snow), with tours running every half hour or so from mid-morning to late afternoon, and there's a modest admission fee (tickets via Recreation.gov). It stays a chilly 40 degrees year-round, so bring a jacket and good walking shoes. Importantly, to protect the cave's bats from white-nose syndrome, you may not bring in any clothing or items (boots, hats, bags, cameras) that you've worn or carried in any other cave or mine.

The scenic drive up from Bear Lake through St. Charles Canyon is gorgeous in its own right. Pack a jacket, sturdy shoes, and your sense of wonder, and Minnetonka Cave delivers one of Idaho's most memorable underground experiences.