The sun blazes low over Prague, gilding the gothic spires of the Old Town. It's the hottest April day since 1800, and the very stones are pulsing with unseasonal warmth. Into this 90F heatwave, Prague's cityfolk are preparing to launch a bonfire. It's unfortunate timing – but it's Witches' Night, and everyone knows you can't dispatch a hag without a fire.
Pálení carodejnic – the burning of the witches – is the ultimate in charmingly wacko holidays, a pagan farewell to the spirits of winter which the Czechs inherited from their ancient Slavic forebears. These ancestors believed the forces of darkness were at their peak on 30 April and in the absence of holy water (not invented yet), hoped to purge the earth of evil by burning a witch in effigy. Apparently no one saw the irony in trying to repel the demonic hordes with a big old fire.
Back to the present day and Prague's Witches' Night combines the costumed creepiness of Halloween with the alcoholism of Christmas.
My witch burning of choice is a family friendly barbecue on Kampa Island, a city-centre oasis in the Vltava River. It starts with a parade of magical creatures and by 7.30pm an expectant gaggle of witch-watchers has gathered in the shadow of the Charles Bridge.
"Can you hear … something?" a student-aged German girl asks. Suddenly, I can. A deep, pacy bongo beat is echoing from Malostranské námestí, the Lesser Town Square. And then, with a whoop, the wild rumpus descends: a cackling, broom-toting, horn-blowing crone conga is dancing its way towards us.
Toddlers ride by on parental shoulders, brandishing plastic pitchforks. A fiend swoops on a bystander, provoking: "Oh my God!" and a dropped ice-cream. It looks like the cast of Narnia got boozed and raided a goth jumble sale. Within minutes a crowd has joined the dance like rats after the Pied Piper.
At the front of the parade, a dummy witch is trussed up on a stick. Next in line is a sort of Vegas Satan in a red satin hood. He's pushing a cart containing a shrieking woman and several small children. The woman (witch, of course) rattles her manacles and screams: "I am innocent," while the kids sit quietly by, all oversized cloaks and stop-it-mum eyes.
Stomping in time to the drumbeats, the crone army moves down Ulice na Kampe, the street that links the Charles Bridge to the Kampa Park. This is the place where the witch will meet her fiery end – and everyone else will eat hotdogs. A folk band is playing wild gypsy music as the event's organiser, Miroslav Stejskal, makes his way to the stage. For 364 days of the year, Stejskal is director of police in the Prague 1 district. Tonight, he's a medieval MC with an executioner's robe and mad-monk demeanour.
"I call all the witches," he bellows. "I ask you, should we grant her a pardon, or will she be executed?" About half the crowd raise their hands for mercy.
"My friends, all of you who raised your hands will lose them." Two things are clear: Czech police are not to be trusted, and the hag's going to burn.
The rag doll is perched above a jenga-like lattice of logs, and the sound of bongos rolls again as the chief witches dance around it. Onlookers jostle for position and smoke pours into the gathering dusk as first the wood, then the witch succumb to the flames.
And then, something happens.
Across the park, sausage sellers cease their sizzling. Portly papas put down their beers. Candy floss blows away, unmissed. To my left, a pensioner puts an arm around her granddaughter, pulling her close. We are as mesmerised as the pre-Christian shepherds who began this ritual, in thrall to the beauty of the burning pyre. Fictional ghouls hold little horror for Czechs who remember the suppressions and show trials of communism, but perhaps it's no surprise that Witches' Night attracts so many of them.
Under the cobwebs and false noses, this is a celebration in which evil is purged and spring rides to victory, renewal on her mind. The Witches of the Kampa have live music, umpteen barbecues, fire jugglers, and enough home-brew to last out the hottest of nights. Were I the cackling type, I'd quit the coven at once and join the party.
• Wizz Air (wizzair.com) flies direct from Luton to Prague from £50 return. The Corinthia Hotel Prague (+420 2 6119 1111, corinthia.com) provided the accommodation. Doubles for April 2013 cost from €99 B&B
