But just as the party is getting going, the weather turns. People laugh when the rain starts, then cover their heads with towels and bags of wine when it begins to hail. A few claps of thunder are enough to send most scrambling for their tents.
The rain never lets up, and the party must wait for another night.
And there will be another night, another party, at what is quite possibly the most crowded wilderness locale in Colorado: Conundrum Hot Springs.
It's a natural wonder in a stunning setting, quite possibly the last of its kind in Colorado, hot pools on public land with free, unlimited access.
How long it stays that way remains to be seen. The U.S. Forest Service says it's being loved to death, and officials are studying options to address the overuse, including an alternative almost unheard of in Colorado: reservations to visit a national forest.
10 a.m. Friday
The parking lot isn't full, but it's getting close. Soon people will be parking along the highway and walking an extra mile on a dirt road.
The Conundrum Creek trailhead is only 5 miles from Aspen, which in high summer is humming with tourists. But the long approach keeps most day hikers away from the hot springs and brings out plenty of first-time backpackers. Some, like the two tie-dye-draped girls from Pennsylvania who are planning to do the hike barefoot, underestimate the challenge.
A man who identifies himself as Tec Cornell from Colorado Springs did the hike in sandals. His friend turned back, he says, because "he thought a 9-mile hike was more like a 5-mile hike."
It's not that the hike is incredibly tough. The Forest Service rates it as "moderate," with 2,500 feet of climbing. While unceasingly uphill, it's rarely steep, with inspiring views of the Elk Mountains to distract your eyes. Most hikers reach the springs in four to five hours, though it took a family from Florida, not used to the elevation, seven hours.
When you reach the pools, set up camp and immerse yourself in the warm, soothing gift from the geologic forces that shaped the surrounding peaks, all the rigors of the day melt away.
The hot springs are unofficially clothing-optional. The largest pool is also the hottest, while three other smaller lukewarm pools, which are clear before you get in but instantly turn to mud, beckon privacy-seekers.
"The last 10 minutes was the worst part," says Anna Parvish, also from Colorado Springs.
"It's worth it," says Cornell. Then, deciding such an endorsement might bring more people, he amends his response.
"Absolutely it isn't worth it. I want to keep this great place to myself."
7 p.m. Friday
Every campsite near the hot springs has been full for hours, but still the line of traffic comes.
Camping is allowed only in the 18 designated campsites. The six nearest the pools, in tree clumps above the springs, have been taken since midafternoon, as late-comers scour the woods below the springs and the tundra above for a flat spot to pitch a tent.
The hot springs saw 3,261 visits in 2012, all but a handful during the crowded summer months.
"All summer long, every weekend up there, Friday and Saturday night, we're over capacity," says Andrew Larson, White River National Forest wilderness ranger, by phone a week later.
The name "Conundrum" comes from early-day miners, who found gold in the stream but never could locate a profitable bonanza. Forest managers have been in a conundrum over the springs ever since.
A bathhouse was built and then demolished. Last year, after several cows froze to death in a former guard station, the roof was removed to hasten the building's demise and discourage what the Aspen Times called "slumber parties."
"We never provide shelter in wilderness. Wilderness is for your own outdoors experience and it's not meant to be a place where shelter is provided," Larson says. Dogs were banned in the area and campfires restricted to campsites well below the pools. In recent years, officials built a kiosk with portable toilet bags, hoping hikers would be willing to carry out their human waste. Larson estimates one in three hikers use them.
"You just think about over 3,000 user days up there, and that's all within a quarter-mile radius of a really wet alpine environment," Larson says. "When I think about 3,000 user days, I think about 3,000 poops in the woods in that small area."
10 a.m. Saturday
Evan Ravitz has been coming to the hot springs since 1978.
"The only thing that's really changed in 35 years is more signs and this clothing rack," said Ravitz, of Boulder, part of an informal group, Friends of Conundrum Hot Springs, that does trail work, maintenance and cleanup.
He comes for the peace, quiet and to meet all the "pretty happy" people who make the hike. Unless you're there in the middle of the night or you ski or snowshoe in winter or spring, visiting is a social experience.
While he has seen use increase over the years, he vows to fight any effort by forest managers to limit the number of people with mandatory reservations. But he fears the Forest Service plans to do just that.
"Their policy for many years has been to let problems accumulate so they can swoop in with draconian measures," he says.
Larson says the agency plans a "conversation with the public on how we want to address the overuse of Conundrum," but permits and reservations would require a lengthy public process.
While rare in Colorado national forests - only the Indian Peaks Wilderness near Denver limits users - he says it is common in other places, such as California.
As the day wears on and the sun beats down, few people use the hot pool, instead taking day hikes to Triangle Pass in the basin above, hiding from the sun in the smaller pools, which offer some shade, or relaxing in tents and hammocks.
Later, two Forest Service rangers stop by to show the bag of trash they collected and remind everyone about the toilet bags. They're roundly ignored by the growing crowd of bathers as the sun slips low behind towering ridges and monsoon rain clouds build in the sky.
11 a.m. Sunday
It's still raining.
A dreary procession winds down the muddy trail, packs heavy with wet tents. Conundrum Creek, which required a simple rock-hop to cross Friday, is now a raging brown torrent. If there was ever a bridge, it has long since been washed away.
A dozen backpackers, many of them first-timers, mill about, unsure what to do.
More experienced hikers pull everyone together into a human chain and, working together, the group makes it safely through the frigid, waist-high water. Strangers hug and shake hands, then continue the long march back to home, jobs and families.
They aren't litterbugs or rule-breakers, just people who shared a weekend at one of Colorado's loveliest spots and banded together to ensure everyone made it out safely.
Maybe this same sense of teamwork and backcountry community will be enough to keep Conundrum Hot Springs unfettered and free.