Known to locals as the Spider Caves, the McKinney Butte Lava Tubes are a large, easily explored lava-tube system out on the high desert near Bliss, in the Gooding, Idaho area. A lava tube forms when the surface of a lava flow hardens into a crust while the molten rock beneath keeps flowing and drains away, leaving a long hollow tunnel behind; here you enter through a collapse in the side of the tube, and the passage forks almost immediately into two branches.

The tubes are the handiwork of McKinney Butte, a broad shield volcano that last erupted roughly 52,000 years ago. It's a geologically rich spot — pillow basalts can be found nearby — and the caves are old enough and tough enough to have survived both the cataclysmic Bonneville Flood some 17,000 years ago and the 1993 Bliss Landslide. The main passage is spacious and open to everyone; bring good light and you can explore a surprising amount of it.

One branch is gated and off-limits without a permit. The tunnel to the right is closed by a gate, and going beyond it requires a permit from the Shoshone BLM Field Office. The reason is conservation: these caves provide critical winter hibernation habitat for Townsend's big-eared bats, a BLM-designated sensitive species that can be harmed or killed by disturbance while hibernating. Respecting the gate — and never disturbing bats anywhere in the caves — helps protect a fragile population and slows the spread of white-nose syndrome, the disease devastating bats across the country.

Getting there involves a drive out Highway 46 onto the desert flats; there are no services nearby, so top off your gas and water first. It's remote, quiet country, and many visitors make a day of it, pairing the caves with the other volcanic features and lava tubes scattered across southern Idaho's black-rock desert.

The nickname “Spider Caves” hints at the character of the place — and, yes, at the spiders and other creatures that shelter in the cave mouths — but the open left branch is a big, walkable tube that rewards the curious with the strange, sculpted textures of cooled lava: ropey floors, shelf-like ledges, and a ceiling that arches overhead. Southern Idaho is riddled with tubes like these, and for thousands of years Native peoples used the naturally frigid caves as refrigerators, caching food and even ice deep in the dark where it kept through the summer heat.

Standard cave sense applies: bring at least two light sources per person, wear sturdy shoes and a warm layer (lava tubes stay cool year-round), and watch your footing on the rocky, uneven floor. To help protect the bats, decontaminate gear that's been in other caves, take nothing, and leave the tubes exactly as you found them. For anyone who loves geology and a good underground ramble, the Spider Caves are a memorable stop in Idaho's volcanic outback.