(CNN) -- Beneath the streets of Budapest, behind the locked door of a brick cellar that smells faintly of mold, four tourists are trying their hardest to break out.
In the room with them are various vehicle parts, a computer and a walkie-talkie, which their captor uses to taunt them as a timer counts down their remaining seconds.
"You can't manage to get out on your own," says Attila Gyurkovics, watching the futile efforts of his four captives via video surveillance.
It may sound like their vacation has gone terribly wrong, but the four have actually paid to be incarcerated and, it seems, they're enjoying themselves.
This is the subterranean world of escape games, a craze that's swept through Budapest.
The games see participants pit their wits against a series of mental and physical challenges in order to gain their freedom in the quickest time possible -- under the watchful eyes of an all-powerful gamesmaster.
Though escape games are now appearing across Europe, Budapest claims to have pioneered this unlikely new entertainment.
What it takes to play
The city now hosts nearly 100 versions and the activity is listed as a top attraction on Tripadvisor.
Typically, participants find themselves locked in two or three semi-derelict rooms in a Budapest basement.
There they must search for keys and clues that will trigger the mechanisms that will free them from the labyrinth.
"It's really fun, you get absorbed in the story and forget about the rest," says Audrey, from France.
She's emerging from one of three separate challenge zones at Parapark, an escape game hidden beneath Gondozo, one of Budapest's so called "ruin bars" (4, Vajdahunyad Street, Budapest; +36 30 619 5447).
Parapark, the domain of gamesmaster 38-year-old Gyurkovics, lays claim to creating the phenomenon in 2011.
"Parapark is really for everyone," he says, keeping an eye on a monitor on which his four captives are still trying to solve a mystery based around a driving lesson.
"Kids from 12 or even smaller can already play. An intellectual and someone who's never been to college can perform equally well."
Gyurkovics, who studied team-building strategies at university, says he devised Parapark as a way of testing group dynamics.
He says there's a need to strike a careful balance to engage participants without overly frustrating them.
"Tasks should be neither too easy nor too hard," he says. "First you think it's impossible to solve the puzzle, but at the end of the day you manage to pick up the elements you'll need to open the exit door."
Flirting with the horror genre
Two months after Parapark was launched, the former social worker quit his job to focus on his new creation.
"It looked clear that I would be able to make a living out of escape games," he says.
He's since hired five employees and begun franchises abroad -- a smart move given that he faces stiff competition from rivals.
Budapest now offers escape challenges for all tastes, most costing about $40 per group of two to six people.
Some, such as Underground Fear (3 Barcsay St., Budapest; +36 20 528 2191) flirt with the horror genre.
In a high-ceilinged cellar just off Budapest's luxurious Andrassy Avenue lies Trap (20 Paulay Ede St., Budapest) an escape game that recently topped TripAdvisor's list of attractions in the Hungarian capital.
Featuring a well designed medieval gallery on one side and an Egyptian pharaoh-themed sliding door challenge on the other, Trap welcomes about 200 groups a month -- 90% of them from abroad.
Its founder, former logistics company owner Zoltan Kovacs, is also pushing beyond Hungary's borders with tracks planned in Prague and Berlin.
Coming back for more
"The phenomenon has its seasonality, but we're keeping on expanding," he says.
Escape games seem to be sound investment in Budapest, where real estate is cheap and low-cost labor is abundant -- not to mention the huge visitor numbers the city attracts.
Kovacs says his two challenge zones at Paulay Ede street cost him roughly $22,000.
The investment appears to be paying off.
"Two years ago my mother thought I was absolutely crazy but now she has changed her mind," he says.
As he chats, one of Trap's challenge doors opens and four British tourists, Omid, Leo, Jason and Ben, emerge from what they say is their second visit.
"We loved it," says Ben. "I'm amazed we did so well! You have very little time to think ahead who would do what.
"We'll definitely come back."
Back over at Parapark, Gyurkovics's four captives are still struggling with their driving test challenge.
He picks up his walkie-talkie to offer the kind of sage advice you'd expect from someone responsible for creating what may soon be a global phenomenon.
"You need to play as a team. And use your brain! You have to be on the lookout for clues."
CNN Travel's series often carries sponsorship originating from the countries and regions we profile. However CNN retains full editorial control over all of its reports. Read the policy. Helene Bienvenu is a photojournalist and travel writer based in Budapest. She's a blogger at Spotted by Locals and the author of several guidebooks on central and eastern Europe. She tweets at @bienvenuLN.