Subterranean lava flow formed this mile-long cave roughly 700,000 years ago. Once you descend into its boulder-strewn maw, the cave is spacious, with 40-foot ceilings, but claustrophobes take heed: about halfway through, the cave tapers to a 4-foot-high squeeze that can be a bit unnerving. A 40°F chill pervades the cave throughout the year so take warm clothing.
To reach the turnoff for the cave, go approximately 9 miles north of Flagstaff on U.S. 180, then turn
west onto FR 245. Turn left at the intersection of FR 171 and look for the sign to the cave. The trip is approximately 45 minutes from Flagstaff. Although the cave is on Coconino National Forest Service property, the only thing here is an interpretive sign, so it's definitely something you tackle at your own risk. Pack a flashlight (or two).
FR 171B, Flagstaff, Arizona, 86001, United States