Wintermas has come to Phantom Peak; Father Platmus is around town in his purple attire, and there's a new mystery to solve about the parentage of unhinged Mayor Pocket.

If that sounds weird and crazy, then it's a bit how it feels to enter this immersive open-world experience.

Somewhere round the back of a huge Decathlon in Canada Water, we found a portal into a steampunk town where the aesthetic of the American frontier collides with retro-futurist technology of 50s TV shows, 70s gaming arcades, and a healthy dose of British quirkiness.

Father Platmus in his grotto at the Phantom Peak immersive game world.Father Platmus in his grotto at the Phantom Peak immersive game world. (Image: Alistair Veryard)

The town is run by the mysterious Jonas, head of the Jonaco corporation, and your ticket buys a four hour visit as a 'tourist' to follow a series of 10 adventure trails.

Of course there are places for a pitstop, at the Frontier Saloon or food outlets. Stuffing yourself with doughnuts, burgers (very good) hot dogs, or the rest of the American-style fare will fuel your hectic hurtle around the site following real world clues with promptings from your phone via the website.

Log on, choose a mystery or an adventure and you might be directed to find an ad on a noticeboard, or watch a clip on Jonasvision to set you off on a mission.

You can take a pitstop for drink or food during your four hour visit.You can take a pitstop for drink or food during your four hour visit. (Image: Alistair VERYARD)

That might involve interacting with one of the townsfolk; postmaster, shop assistant, Pius from the Church of the Cosmic Platypus (!), cinema usherette, mayor, undertaker, evil Dr Winter, or fairground barker.

Or it might involve solving a cypher, shooting hoops at a carnival, researching in the archives, playing a videogame, or searching a graveyard of tombs for clues.

The trails change every few months and it can't be easy coming up with satisfyingly knotty storylines. In truth, not all the trails are equally riveting, there was one about Quantum Mechanics that we swiftly abandoned, but another about a murdered Muppet-style character was great fun, and the puzzle around The Mayor's parentage was involving.

The closing Wintermas ceremony at Phantom Peak.The closing Wintermas ceremony at Phantom Peak. (Image: Alistair VERYARD)

Like a lot of self-guided experiences there's the FOMO of feeling everyone else is on a more thrilling trail than you. We spent a while wondering how to get to the town grotto or maze, then just took ourselves off to investigate.

To get the most from the experience you have to enter the spirit of the game, whether that's improvising with the admirably committed actor/characters, working out the clues, or singing along to the silly Platmus Christmas song at the closing ceremony, which ends in a flurry of snowfall.The Closing ceremony at Phantom Peak.The Closing ceremony at Phantom Peak. (Image: Alistair VERYARD)

There's a competitive element, you get a card when you finish a quest, and the keenest among your fellow gamers were vying to win a badge.

I took along a teenager who threw herself into the missions - but really Phantom Peak would appeal to everyone from 10-100.

The town is now decked out with festive lights and fir trees and would make a great alternative Christmas outing. Don't forget to try one of the Wintermas cocktails which have a distinctly festive twist, flavoured with cinnamon, egg nog or dressed with candy canes.

Wintermas at Phantom Peak runs Thursday to Sunday. Adult tickets start at £42, children aged 4-16 are £20 and young adults 17-25 are £30.