The closest cave to Keystone and to Mount Rushmore is Rushmore Cave (13622 Hwy. 40, 605/255-4384, www.beautifulrushmorecave.com, June–Aug. daily 8 a.m.–8 p.m., May and Sept.–Oct. daily 9 a.m.–5 p.m., closed in off-season), located about five miles east of Keystone on Highway 40. Discovered in 1876 by gold miners digging into the mountain to find a water source to bring to their mine below, the cave was opened to the public in 1927.

Two tours are available. The standard one-hour tour costs $12 for adults and $7 for children aged 5–12 years. The 2.5-hour Adventure Tour (daily 10 a.m. and 3 p.m., $30) explores locations in the cave accessible only by crawling through tight passageways. Helmets, headlamps, knee pads, and elbow pads are provided. The tour is limited to five participants, all of whom must be at least 14 years of age and must sign a liability waiver.

It contains a nice array of stalactites and stalagmites and the path through the cave is well maintained and well lit. There are several different cave rooms on the tour; the “Big Room” is impressively large and filled with interesting formations. It’s a fun and interesting tour.

Caves remain very cool, generally around 58°F even in the hottest part of summer, so you’ll want bring a sweatshirt to keep warm.