South of the Sun Valley area, Hwy-75 runs across 60 miles of south-central Idaho’s rocky black lava flows. Halfway between Sun Valley and Twin Falls, eight miles north of the town of Shoshone, the Shoshone Ice Caves (daily in summer; $6; 208/886-2058) present a series of lava tubes developed into a low-key tourist trap. Just west of the highway, their constant cool temperatures (as low as 28°F) do make a pleasant contrast to the often-scorching summer heat. (The “ice” in the name is created by air currents flowing through the tubes, causing subterranean water to freeze.) The only way to explore the caves is through guided tours, which take about 45 minutes. The gift shop and mineral museum will satisfy anyone’s needs for tourist-trap trash.

  Just down the road, Mammoth Cave is much more basic and undeveloped; for serious spelunkers, there are over a dozen other caves and lava tubes nearby. Contact the BLM office (208/732-7200) at 400 W. F Street in Shoshone for details.

  The only town along this stretch of road, Shoshone (pop. 1,395) is a ranching and railroad center that marks the junction of Hwy-75 with US-93. Some of its buildings have been constructed from local volcanic rock, and though it’s a fairly timeworn place, Shoshone looks great at sunset, when its steel water tower glows and places like the neon-signed Manhattan Cafe (208/886-2142) along the railroad tracks look especially appealing.