I have seen grownups gleefully make dinosaur masks from markers and paperboard — and wear them.

I have seen dinosaur onesies and a dreadlocked paleontologist’s namesake dino tattoo.

I have watched a man craft a fearful Spinosaurus from hundreds of yellow balloons (he had lost count) before I wandered into a room where a downcast DJ played David Bowie for hollow-eyed Hadrosaurs and a dance floor of five.

I ate a hot dog. I held dinosaur poo. I hit the bar, missed the s’mores and was told a fossil-hunting bedtime story.

I experienced childish wonder and serious air-mattress envy during the ROM’s first ever adult sleepover.

The Royal Ontario Museum has been hosting popular kids’ sleepovers since 2008. The Jan. 15 event, dubbed “Dinos in the Dark,” was the first of its kind for a 19+ crowd.

“Museums should always try to engage with their audiences in new and interesting ways,” Erin Kerr, the ROM’s adult program coordinator, told me. “We often assume that adults won’t want to have fun in the same way as kids do, and that’s not true.”

Like adult colouring books and summer camps for grownups, the event catered to a growing childhood nostalgia fad. You could see it in the stockinged feet, flannel pajamas and sweetly eager smiles so many participants wore — participants who shelled out $225 for tickets (or $200 for members) on the promise of food, booze and music paired with all kinds of Mesozoic fun.

Couples young and old, groupings of women and a few lone souls made up the crowd of 60 or so people. Like the ROM’s family-friendly events, interactive play was prominent.

“You can learn a lot from poo,” Toni Largo said as I handled a hard prehistoric lump. The ROM teacher had fossils and casts out on a table for hands-on guessing games. Largo says she almost always works with children.

“Who asks better questions?” I asked.

“Kids,” she said. “They have no limitations.”

At the bar, Peroni is all they have for beer. Kathy Zadvorny and Melissa Whitman are wearing their newly crafted dino hats. The two had driven up from Hamilton to celebrate Whitman’s 40th birthday.

“We were making these and suddenly an hour went by,” Whitman said with a laugh. “I think people just forget to have fun.”

As a DJ played everything from Bowie to Blackstreet, My Beloved Brontosaurus author and amateur paleontologist Brian Switek sipped a drink under a T. Rex-like Allosaurus skeleton. The museum had flown him up from Utah to sign books and chat with patrons over the weekend. He rolled up his sleeve to show off an Allosaurus tattoo.

“It’s always been one of my dinos,” he said with a smile. “They were discovered more than a century ago, but not a lot of people studied their biology — how they lived. I promised myself to find out more about them.”

It was wonderful to wander the near-empty dinosaur galleries, drink in hand, while music wafted around the skeletal remains of beasts that roamed this planet before humans were a dream.

By the time I made it back to the sleeping area, it was past 1 a.m. Night at the Museum was playing overhead for a pajama-wearing, popcorn-munching crowd. From a bouncy air mattress in the centre of the room, Beth Laidley and Jasmine Kochar watched the film in dinosaur onesies complete with toothy hoods and spiky tails.

“I ordered them specifically for this,” Laidley said.

“We’re not dinosaur-crazy people,” Kochar added with a laugh. “But this sounded like fun!”

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When the movie finished, Dr. David Evans took the stage as a yule log burned on a giant projector screen behind him. The ROM paleontologist told a story of how he discovered the oldest known dinosaur nursery.

“They would come back to the exact same site year after year after year to lay their eggs — very much like modern birds.”

Before saying goodnight, Evans warned us about Charles Trick Currelly — an obsessive orientalist and long-dead ROM curator who haunts the museum.

“Don’t tell us that!” someone shouted from their sleeping bag. Evans laughed.

“If you don’t believe me, talk to the security guards here.”

It was 2 a.m. The lights were switched off. I tossed and turned on my thin foam mat as security guards circled the sleepers. I couldn’t remember the last time I felt so supervised.

I didn’t see a ghost.

But it was a shock when the lights came on all at once at 7 a.m. Chatter, groans, the hisses of deflating air mattresses. I felt the subway rumble underneath. Stiff and bleary-eyed, I packed up my gear and skipped “Dino Themed Yoga.”

I caught up with Zadvorny and Whitman in the gift shop.

“That was fun,” Whitman smiled. “I’m glad we were the trailblazers!”

I asked her if she’d do it again. She laughed.

“It was a good thing to do once.”

The next ROM adult sleepover will be held in September. The event will focus on two upcoming exhibitions: the colourful glass art of Dale Chihuly and “A Third Gender: Beautiful Youths in Japanese Prints.”