Smith's Crack is one of the most unusual — and most demanding — caves near Mountain Home, Idaho. Unlike the region's many walk-in lava tubes, this is a lava fissure: a deep crack that opened as a lava flow cooled and contracted, leaving a narrow, vertical, maze-like cave that plunges toward the bottom of the flow. It's a genuine adventure and a local favorite among experienced cavers, but it is emphatically not a beginner's cave. (You may also see it labeled “Devil's Hole” on some maps — a misnomer for this same fissure.)

From the entrance near one corner of the opening, the route works its way down and through a series of rooms and passages. For the most part arrows mark the way, but the entrances and exits between chambers can be genuinely hard to find, so plan on spending a couple of hours underground. Just before the cave bottoms out at the base of the lava flow there's a serious 20-foot vertical drop; from there the passage gradually regains elevation and eventually leads to an exit about 100 yards north of where you started.

Take the danger seriously. Cavers who've done Smith's Crack describe it as thrilling but no joke — there are multiple drops and climbs where a slip or a grabbed loose rock could cause a serious or even fatal fall. Add in slick surfaces, tight squeezes, and the disorientation of an underground maze, and this is a cave that demands real caving experience, good judgment, and ideally someone along who already knows the route. It should never be a first cave, and no one should go alone.

A few specific cautions from those who've been: don't go during wet seasons, when the rock is slicker and conditions more dangerous; wear a helmet and gloves and use sturdy footwear; and be ready for the grime — the cave collects bird droppings, fungus, and unfortunately some trash, and snakes have been seen near the entrance in warm weather. Bring at least two reliable light sources per person, since it's pitch dark and both hands are often needed to climb.

A bit of geology makes the visit richer. Fissure caves like Smith's Crack are relatively rare compared with the walk-through lava tubes that dot the Snake River Plain — they form along cracks and faults in the cooling basalt rather than from a drained lava river, which is why the passage is so vertical and maze-like rather than a simple tunnel. That character is exactly what makes it thrilling for experienced cavers and dangerous for the unprepared.

Come prepared, go with an experienced group, tell someone your plans, and follow the arrows carefully both in and out. For skilled, careful cavers, Smith's Crack delivers a genuinely exciting descent into Idaho's volcanic underworld — but it rewards respect and punishes carelessness, so treat it accordingly, and help keep it clean by packing out everything you bring.