Seventeen Mile Cave is an easy, family-friendly lava tube out on the volcanic plain about 17 miles from Idaho Falls, Idaho — the source of its name. Formed by the flowing lava of the Snake River Plain's volcanic past, the tube was left hollow when the molten rock drained away, leaving a tunnel you can walk right into. Its easy access and gentle floor make it one of the most popular beginner caves in eastern Idaho, drawing spelunkers from Idaho Falls and Rexburg alike.

The entrance sits just a few hundred feet from the highway, and the cave runs a little less than a quarter mile back. What sets Seventeen Mile Cave apart from most lava tubes is its floor: instead of the usual jumble of collapsed rock, much of it is smooth and nearly flat, which makes walking the length of the cave surprisingly easy. There's one main tunnel that's simple to follow — no real chance of getting lost — making it a great first caving trip for kids and newcomers.

At the far end, the quarter-mile passage finishes at a pair of small pools and a swampy area; it's difficult to push much beyond this point, so most explorers turn around here. Along the way, the cave stays cool and humid year-round no matter how hot the desert above, so it's a refreshing escape on a summer day — and a genuinely chilly one in the shoulder seasons.

Come prepared with the caving basics: bring at least two light sources per person (the cave is completely unlit), wear a jacket or extra layer for the cool interior, and put on sturdy, closed-toe shoes, since the floor is damp and can be slick near the pools. It's a short trip, but a headlamp that frees your hands makes it far more enjoyable.

The cave is one of many volcanic features scattered across this stretch of the Snake River Plain, a landscape built by ancient eruptions and riddled with tubes, cracks, and cinder cones. That makes it a natural first stop for local families and Scout groups getting into caving, and an easy add-on to a day of exploring the wider volcanic country around Idaho Falls. Bring a group — caves are always more fun, and safer, with company — and let someone know where you're headed.

One honest note: because it's so close to town and so easy to reach, Seventeen Mile Cave gets heavy traffic, and it shows — the walls carry a lot of graffiti and the floor collects litter. Do the cave a favor by packing out everything you bring (and maybe a bit extra), skipping the spray paint, and treating the place with respect, so this accessible little lava tube stays a fun introduction to caving for the next family that comes to explore.