I’ve just ordered a beer when we’re warned there’s a werewolf on the loose. A sweaty, spiky-haired man in a black robe bursts through the tavern doors, waving his plastic wand. “Everyone to your common rooms!” he shrieks. The room empties.

My friends think I’ve gone to a role-playing sex party. They’ve heard I’m spending the weekend at a Polish castle dressed as a schoolgirl wizard with more than 100 strangers. We’re going to put hexes on each other and sleep in mixed dormitories. I know how it sounds. But the College of Wizardry is a Larp, which stands for live-action role play. There are 140 “players” from 29 countries, joining an unofficial re-creation of the magical world of Harry Potter.

Only, it’s not Harry Potter. It’s a knock-off version that doesn’t outwardly reference Harry, to keep Warner Bros and JK Rowling sweet. There is no Ron or Hermione. No muggles, only “mundanes”. We are warned that if we use the spells from the books, or the real house names, “a man in a suit will appear and drag you away”.

That hasn’t stopped the hardcore fans. A blonde woman in dark lipstick called Marie says she quit her job in America to be here, and this is her second time at the college, which has been running since 2014. “You don’t know what you’ll find out about yourself,” she tells me in our dorm, where a 30-something man is putting on his shorts and a tie.

I haven’t played make-believe since primary school, but this weekend I’ll be “a first-year witch from Iceland with a mysterious past” – I’ve been sent a briefing in advance. I’ll be expected to eat, breathe and sleep as her for two and a half days.

In the great hall of the 13th-century Czocha Castle in southwest Poland my fellow Larpers compare their handmade props and excitedly discuss the agenda. The crowd is a curious split between geeks and those who say they had never heard of a Larp until they came across the College of Wizardry on BuzzFeed.

From a balcony overlooking the long tables in the hall, we’re greeted by the college’s headmistress. “It’s time to leave the mundane world outside,” she booms, her hair in a Professor McGonagall-style bun.

Then we sing the “school song” from printed sheets. We eat Polish food together while people dressed as ghosts, goblins and teachers filter around the tables. We try to stay in character and keep the small talk going, and we drink. This helps.

After an awkward first hour, I meet a wild-eyed “witch” called Hannah. “Do you want to find the secret passageways?” she says. I assume it’s not a come-on so I roll with it and we discover bookcases that lead to dungeons and parties in full swing. We stop to chat to preposterously severe “prefects” patrolling the corridors and shy first years in gold-buckled shoes and felt hats. One is clutching a fluffy mouse pencil case as a pet, which we poke with our wands. I’m starting to have fun.

Back in my dorm, some people are already asleep. A bald man in harem pants, with a dot pattern drawn on his head, is doing some stretches. “Night,” I say as I tiptoe around him.

We wake the next day to a timetable of lessons. “Alchemy” is the most enjoyable. We mix potions from bubbling pots and smoking vials in a dimly lit stone cellar. The atmosphere is as immersive as any Punchdrunk theatre production.

Later, I meet Claus Raasted, the organiser. He says that 40% of the participants have never done a Larp before. Through a crowdfunding campaign his colleague Maury Brown is now holding a similar event, Magischola, on a college campus in Virginia this summer. The first dates have already sold out.

Back in the common room, things start to get weird. An initiation ceremony requires us to “cut” our hands with our wands and drip our imaginary blood into a bottle of wine. Then we must drink from it. I become quite desperate to know what my friends are up to back home.

The next day, I start to break rules. I speak out-of-character to Magda, a Polish psychologist whose ticket was a present from her colleagues. She has had enough. The two of us take a walk outside. Senior students are having a “battle” in the forbidden forest, chasing someone in a beast costume. This is quite beyond the silly Harry Potter stuff we were expecting.

As we dress for the ball that night, Marie gives me the heads-up. “On the final night it gets crazy,” she says. “People get wasted, they drink, they dance, they screw in the hallways.” We have to bring a date, so I find the guy with the fluffy mouse toy and join the couples waltzing in the hall. Thankfully the night is more school disco than sex cult.

Later, the music changes from Chopin to Calvin Harris and I’m relieved the pretence is over. “I’m a hotel manager from Shropshire,” says a woman who had earlier insisted she was descended from a long line of dragon-tamers.

On the bus back to the airport, I feel tired in the same claustrophobic way I did playing games as a child. I’m glad to have met some of these unusual and inventive people, but it’s safe to say I won’t be graduating to “second year”.

Essentials

Sign up to the waiting list for the 7-10 and 21-24 April College of Wizardry events at cowlarp.com. Tickets are still available for the 24-27 November event and there is a waiting list for 17-20 November. College of Wizardry costs €375, which includes accommodation and food at Czocha Castle from Thursday to Sunday. Fly from London to Berlin with easyJet from £25.49 and take the ‘Witch Bus’ from Schönefeld and Tegel airports for €50 return