It’s 8:00PM on a Saturday night in mid-July and I’m standing in chest-high river water, attached to an inflatable float, alongside a man dressed like an aquatic Arabian prince. I’m here, in this undisclosed location — namely, a dirty river near New York City — because I’ve been invited to a super secret illegal cave party. My Arabian prince host calls himself Baron Ambrosia. (Watch our video above.)

“I was driving on New Year’s Day and saw [the cave] from the street and was like, ‘Holy shit, does that river disappear into a cave?’” Ambrosia says as he lights gas lanterns he’s hung throughout the secret space. “I went and checked it out. Tonight is the culmination of a six-month obsession.”

In, around and beneath this city, there is a group of people who self-identify as urban explorers. They look for all the places the rest of us either don’t see or seek. It takes a special kind to unearth something new and Ambrosia — culinary impresario, filmmaker, artist, ambassador to the Bronx, urban explorer and super secret party thrower — invited ANIMAL to this wooded grotto because he’s launching wine made from a birch tree, called Birch Sap Wine. The entire party will be in the water.

“What’s in the glass should be reflected by the surroundings,” Ambrosia says. “We want to get people the full experience. That’s why we’re going to do this in this wet, watery, cave.”

It’s a tasting party but to access the wine, half-naked women, innertubes, oysters and Ambrosia’s cave of dreams, I had to wade into the cold water that carried a strong current, with rocks littering the sandy floor, and undetermined forms of wildlife within. The cave, which is 125 feet long, 10 feet high and 12 feet wide, is being decorated a few hours before guests arrive. The gas lanterns Ambrosia hang emit an amber glow. He drops glow sticks to the bottom of the river bed then wades over to a shrine of a woman’s head, which is situated across from a floating bar made out of a silver table from a morgue.

“This is not a decapitated… this is not an oversexed female,” Ambrosia tells me as he secures the woman’s floating, glowstick-illuminated head. “This is a Forest Goddess.”

To have the privilege of seeing Forest Goddess and scoring an invite, you must be someone whom Ambrosia deems worthy. You are an artist, a chef, a tastemaker, or a creative and fun person. You know how to navigate illegal parties, which means you know how to keep your shit tight. You like to dress up. And party. But you don’t get sloppy. And you pee downstream (or, at least not in the middle of the party).

Ambrosia’s philosophy: a properly applied space can be more intoxicating than alcohol, drugs or music.

Just around 9:30PM the first people start arriving, wading in with headlamps, flashlights, inflatable tubes, boats, rafts and even canoes. A few days before, Ambrosia and his 64-year-old father, John, an engineer, cleared a path to the riverbank by macheteing through the thick brush. They covered the path entrance with a bushel of branches, which swung open like a door and closed behind you masking the path. Of Ambrosia’s biggest logistical concerns tonight is the abandoned parking lot that will fill up with cars, possibly alerting cops.

In an email he sent out to guests, Ambrosia highlighted the importance of on-time arrival, that someone would shepherd them to the cave, and that they dress up.

“The wardrobe is nymph, satire, Neptune, Poseidon, mermaid, or pixie,” he wrote. “As you will be spending a lot of time in the water, fashion only needs to be from the waist up, waist down is for comfort.”

Within an hour, the length of the cave is filled with people atop floats, smoke from the gas lanterns and cigarettes blankets the air. The biggest challenge is wading from one spot to another, especially if you’re trying to walk. At the height of its capacity — probably around 40 to 50 people — Ambrosia gathers everyone around the bar. He then has someone cut the music and introduces Andreina Veliz, a Bachata singer from the Bronx, to christen the cave with her voice.

The wine (which is sweet from the sap of a black birch tree but also carbonated with bubbles) is tapped from a keg Ambrosia’s business partner, John Chapman, brought from his Rockaway Brewing Company. As wine is passed around, attendees eat oysters, fresh cherries, and brie from the floating bar.

Many people here are Ambrosia loyalists; never missing a party he throws. Samantha qualifies, and she’s here as part of a three-woman crew that floated on inner tubes all night. She runs an event company and all the women were decked out in glitter, fishnets, feathers and beads. She’s well aware that she’s among the elite.

“Nobody knows where I am right now!” she says.

She’s holding a near-empty jug that was filled with homemade whiskey lemonade. She convinces me to open my mouth and pours the final shot down my throat.

I see a dude wearing oyster shells around his neck standing by the bar. Call Nichols offers me the first oyster, which is fresh and salty. Nichols is an aquaculturist at Fishers Island Oyster Farm and met Ambrosia through the Explorers Club. He got here from the city, taking a bus to “the sticks” and then hailing a cab. When he arrived at a random parking lot in the middle of seemingly nowhere, his cabbie kept asking him in Spanish if he was sure.

“Those are the kind of miracles when they actually happen — [Nichols] just enters the party, probably off a city bus, with a fucking case of oysters and his shucking knife — those are the kind of people you want at your party,” Ambrosia says.

A crew from Anthony Bourdain’s production company shows up, tequila in tow as do a Bronx blogger, members of the ZULU nation, a circus performer who eats glass, and associated friends who somehow were fortunate enough to land in Ambrosia’s Venn diagram. No one here is douchey, everyone knows they have it good.

But it’s getting cold and after four hours in the water we start wrapping up. About half the people had already left, but a few more were still coming in. At that point, Ambrosia’s biggest worry was someone dying, monitoring everyone while trying to ensure there won’t be any floaters.

As we were about to go, I see a man wearing a string of blue LED lights around his neck, dressed in a tuxedo wearing a headlamp. He looks like a veteran of this scene. Turns out he is.

“In some very nerdy small circles — in the people who love the underground — in those sorts of circles I’m fairly famous,” says Steve Duncan. “I’m a hero.”

Duncan says it’s one of the best parties and spots he’s ever been to, because he was unaware of the cave’s existence. He hopes people will try and find its secret location so the urban hydrological health of the city will improve. He wants an awareness spread.

“The more people who try and search out where we are,” he says, “the better.”

(Photos: Amy K. Nelson/ANIMALNewYork, Video: Aymann Ismail/ANIMALNewYork)