Niter Ice Cave is a lava tube in the farm country of the Gem Valley, about three miles south of Grace, Idaho, and a few hundred yards east of State Highway 34. From the road it looks like a low rim of dark basalt sitting in a hay field, but the opening drops into a long, cold tunnel where ice builds up on the floor for much of the year. It is one of the easiest lava tube caves in southeast Idaho to reach, and one of the few you can walk into straight from a gravel pullout.

The cave formed roughly 500,000 years ago, when basalt lava flowed across this part of the valley from the direction of Ice Cave Knoll, the small cinder cone on the west side of the highway. As the surface of a flow cooled and hardened into a crust, molten rock kept moving underneath it. When the supply stopped, the liquid drained out and left a hollow tube behind. That is an old age for a lava tube, since most collapse or fill in far sooner, and the stretch you can walk today is a surviving remnant of a longer system that is now mostly buried under wind-blown soil. Southeast Idaho High Country Tourism puts the open passage at about 1,800 feet long, roughly 24 feet wide and 14 feet high.

The entrance is a collapse in the roof of the tube. Cold air is heavier than warm air, so in winter frigid air sinks through that opening and settles in the passage, while summer heat has a hard time pushing in. Water dripping through the basalt freezes in that trapped cold, and the interpretive sign at the site says ice forms in the cave about seven months of the year. By late summer the ice is often gone and the floor turns to mud and standing water instead, so what you find depends heavily on the month.

People have used the cave for a long time. Native Americans and early settlers kept food in its natural cold, and pioneer families in the Gem Valley stored milk and butter there and made ice cream in July. John A. Dalton filed on a homestead next to the knoll in 1898, and local accounts say his family also used the cave as a refuge. Grace residents still repeat a story that community dances were once held in the big room near the entrance. The cave shares its name with Niter, a small farming community about two miles to the south; no reliable record we found ties the name to any saltpeter mining here.

To get there from Grace, drive south on Main Street, which becomes State Highway 34, for about three miles. Turn left (east) onto Ice Cave Road and go roughly 0.15 to 0.2 miles to a small gravel pullout on the north side of the road, right above the entrance. A short dirt path with a handrail leads down into the opening, and a narrow wooden walkway runs a little way into the cave. Past the walkway you are on uneven rock, mud and ice, with piles of breakdown from the ceiling to climb over, and near the back the ceiling drops until the passage ends in a crawl. The tube does not branch, so it is easy to follow, and most visitors reach the end in 10 to 15 minutes.

Bring at least two reliable lights per person, since daylight fades within a few yards of the entrance and a phone light is a poor backup. Wear sturdy shoes with good grip and a warm layer, because the air inside stays near freezing even on hot summer days. The entrance steps are often wet or icy. Graffiti and old fire rings are unfortunately part of the scene; please do not add to them, and never build a fire inside, since the smoke has nowhere to go. In winter, bats may roost in the cave, so keep noise and lights down and leave any hibernating bats undisturbed.

There is no fee, no gate and no posted hours, and the site has no restrooms, water or trash service. The cave sits on land that is not federal; it is not part of the Caribou-Targhee National Forest or BLM ground, and the fields around it are private property, so park only in the pullout or along the road shoulder and stay on the path. The City of Grace and Southeast Idaho High Country Tourism both list it as a local attraction.