Twisted chasms and abysses with eerie formations dripping from rock ceilings and growing from crusty floors await those who venture into Wyoming's underworld.
Bring your own light.
Although not as renowned as the state's above-ground wonders--Yellowstone National Park, the Tetons and Devils Tower, for instance--the grottoes that undermine Wyoming are growing attractions.
But unlike Luray Caverns in Virginia or Carlsbad Caverns in New Mexico, Wyoming's 300 or so caves are not strung with electric lights. There are no walkways or handrails to accommodate tourists.
"This is a wild cave, and we want to manage it like that," said Dave Baker of the U.S. Bureau of Land Management.
Horsethief Cave, located on federal land overseen by the BLM east of here, late last year was designated the nation's first underground recreation trail by the U.S. Interior Department.
The cave twists and dips and rises and falls through roughly 12 miles of mapped passages that snake through the limestone guts of Little Mountain near the Wyoming-Montana border. An additional three miles have yet to be mapped, Baker said.
"Under any given rock there could be a lead that could take you into a lot more cave," said Baker, an outdoor recreation planner for the BLM's Worland District.
To reach the cave's bowels, you have to slink for about 100 feet through "Denise's Crystal Crawl," a tight crevice several feet wide and about 15 inches high in places.
Other snug crawlways await, as do rock chimneys to shimmy up and the 10-foot high "Gypsum Wall," which must be scaled.
The course through Horsethief is a dirty one. The narrow beam from my headlamp separated particles in the cloud of dust that trailed Baker as the BLM caver led me deeper and deeper into the cave.
The thick dust we kicked up soon coated us and added another brown layer to the brilliantly white crystalline gypsum crust covering some of the rock walls we squirmed past.
Until 1970, the cave wasn't thought to be more than just a 700-foot dead end. But when a Laramie spelunker named Denise felt a flow of air from the perceived dead end, she pulled away a few rocks and found the tight crawl that bears her name.
Wayne Sutherland, who led the group that found the crawl, said the discovery spurred many others to head to the cave and search for new leads.
"One of the big sections was found in early 1971 when a group from Montana came in and a fellow was lost, went the wrong way," recalls Sutherland, now an environmental engineer with the BLM in Rock Springs. "In the process of searching for (and finding) him, a large section of cave was found."
A cave discovered in the late 1970s, Great Expectations, is among the most dangerous in the state, according to Sutherland, who co-authored "Caves of Wyoming" in 1976.
"That's a major cave," he said. "It's also a good one to get killed in. Cold temperatures, water flowing through a large portion of it. Probably 37 degrees. Anyone who does much exploration there is going to get immersed."
The cave, on the west side of the Big Horn Mountains near Hyattville, tests the most seasoned spelunkers, Sutherland said.
"It's a very nasty cave, very long, fairly tight entrance to it," he said. "It's a combination of rope work and cold water that really makes it dangerous."
Horsethief, on the other hand, is probably the state's prettiest cave because of its numerous formations, Sutherland said.
Oddly shaped speleothems--mineral deposits formed through the centuries by seeping water--droop from the cave's ceilings, rise from its floors and jut from its walls. One takes the shape of a climber ascending a tower, another juts from a wall like a bat's wing.
Rooms vary greatly in size, from just big enough to sit up in to some the size of a small house. Passageways break off in all directions; some dead-end, some follow the correct path through the cave.
Beyond Denise's Crystal Crawl are the Flying Anvil or Dolphin Room, Powder Mountain, Boar's Head, Mind Bender Pool, Montana Maze, the Crack Where Water Comes Through and many other chambers and tunnels. On some of the walls and rock lips you see reminders that Wyoming was once, eons ago, an inland sea--corals and shells embedded in the limestone.
"This was all underwater, an inland sea. Then it all went away, uplifted," Baker said.