Joshua Sofaer was wandering around a London art gallery recently, minding his own business, when a woman tapped him on the shoulder. ‘Ohmygosh, are you that guy that set up the scavenger hunt in San Francisco?’ shrieks an American accent. When Sofaer nods, her smile drops and she launches into a full-blown arm-flapping rant. Turns out she got a parking ticket that day in the Bay Area, had a fight with a shop assistant, pulled a muscle and ended up exhausted in a heap. ‘But did you have fun?’ Sofaer asks, wincing a little. ‘Hell yeah!’ she squeals back. Apparently she loved the chance to run around getting sweaty, doing something completely out of the ordinary and basically acting a bit mental for a few hours.

Scavengers is Joshua Sofaer’s creation, a day-long treasure hunt against the clock, where the winning team scoops a cash prize of £2000. Having used the streets of San Francisco, Frankfurt and London as his hunting ground, he’s now bringing the action to Edinburgh. Forty teams of four will be invited to join in, and spend nine hours cracking clues that lead to 100 different objects. The items on their oddball shopping list can be begged for, bought, borrowed or simply blagged, but the more points they notch up - harder-to-come-by items are worth extra marks - the bigger their chance of winning.

Sofaer isn’t giving away what Edinburgh teams will need to get their hands on, but previous items have ranged from the arts-and-craftsy to the daft, the beautiful or the downright impossible to get hold of (try getting your hands on a urinal, a double mattress and a horse carved from carrots in the space of a few hours). One of Sofaer’s favourite items from the San Francisco scavenge was, ‘any action figure model that is not Superman, dressed as Superman’.

‘We ended up with Action Man, Bart Simpson, little green monsters and Wonder Woman all wearing Superman’s clothes; it was hilarious, people had gone to so much trouble coming up with something a bit original.’ It’s a chance for teams to get creative, show off their artistic side and get to know undiscovered corners of the city.

After crossing their fingers that the heavens won’t open on the day, Sofaer recommends teams pool their resources by picking a fast runner, a good sleuth and someone who knows their way around an A-Z. Participants are free to dress up if they fancy, and move around on foot, bike, car, scooter, skateboard; whatever covers the most ground quickest. After items are collected that evening, they’ll go on display at the City Art Centre in a week-long exhibition.

‘I like the idea that members of the public can tell their friends they’ve had something on show in a gallery,’ says Sofaer, a London-based performance artist whose work encourages the public to get involved in visual and performance art. ‘I believe in making art interactive and accessible, and always add a sense of humour to what I do. Once they see the list, I’m not responsible for what happens next. I want them to have fun, and also explore notions of what performance and visual art really are.’

When Sofaer took Scavengers to the Tate Modern three years ago, the clues were based around works of art in the building. The final clue, ‘you’ve got to be taking the piss’, led to Marcel Duchamp’s ‘Fountain’, a urinal presented as a ready-made sculpture, the artist’s convention-bending comment about modern art. The only team that managed to source a urinal of their very own got their reward when it took pride of place on its own special plinth in the Tate’s Turbine Hall.

Most of the leg-work and artistic flair will be down to the teams, but Sofaer is also using local Edinburgh actors to act out on-location scenes for the teams to help solve the more cryptic clues. When the hunt finishes, Sofaer will perform at the City Art Centre. He thinks it’s only fair to make a fool of himself, considering the amount of humiliation teams may have gone through by that point. ‘In San Francisco I dressed up in a skin-tight Lycra costume that looked as if I was naked. Some teams had almost been arrested that day; others put up with abuse from people who didn’t have a clue what they were up to, so I had to do my bit.’

Sofaer stresses that he hates sounding ‘grand’ about this kind of thing, but one of the Scavengers aims is to challenge our preconceptions of contemporary art. Once the City Art Centre is full of scavenged treasure - from fruit and toys to tools and hand-made sculptures - is it Sofaer’s art or the teams’? And do items pulled from a skip a few hours earlier even merit a place in an exhibition?

When visitors flooded the San Francisco Museum of Modern Art to view the collection of trash and treasure on display, the general response was very positive. Besides getting a kick out of seeing 70 toy skulls crammed into a glass case, or a wobbly, multi-coloured stack of cardboard shoe boxes next to a pile of plastic hand grenades, one visitor said he enjoyed the ‘blink and you miss it’ feel of the show. If you hadn’t been there on the day to take part, or made it into the museum before the show was taken down (after a couple of days, many edible objects were starting to rot) then you’d lost out on the ‘ephemeral magic’ of the project.

The Anneka Rice-meets-art concept has proved such a big hit since Sofaer set up his first Scavengers at London’s Institute of Contemporary Arts in 2000, that cities all over the world now contact him, trying to lure him to their town to host an urban art adventure. ‘I’ve had to turn most down, as each event involves a lot of forward planning and expense, but when the opportunity to do an Edinburgh Scavengers came along, I had to say yes, mainly for selfish reasons.’

Born in Cambridge, he moved to Edinburgh when he was a few months old and stayed until he was 17. Setting the clues will be a trip down memory lane for him, and he plans to lead teams to a few of his old hang-outs. ‘I remember running around under those big rhododendron bushes in the Botanics when I was small. That could be an ideal place to hide something or someone,’ he says, voice trailing off while his imagination goes to work. Teams might also have to head out of town - to get hold of a Musselburgh speciality or a Pentland memento for example - but they’ll need to decide whether the points they’ll gain are worth the detour.

Sofaer hopes the hunt will attract locals as well as visitors who are in town for the Festival. ‘It would be fantastic if we got a really broad mix of people, maybe a team of doctors, cyclists, art students or tourists; it’d be interesting to see how they each rise to the challenge.’ Whether they end the day with blistered feet and a wad of parking tickets, or finish up two grand richer, hopefully they’ll find a bit of thrill in the chase. They might even hunt out their inner artist while they’re at it.

Scavengers, City Art Centre, Market Street, 16 Aug, 9am-10pm. To take part, register at www.festivalscavengers.co.uk or call 07790 235963. £12.50 per person/£50 per team. Free exhibition at City Art Centre, 18-24 Aug, 10am-5pm; Sun noon-5pm.