Format shows - everyone's doing them. 100 Hours marks a foray by TVNZ into this lucrative arena. A joint production between TVNZ and Holland's IdtV, 100 Hours has "great potential", according to Mark Overett, creative producer, overseas sales.

He should know, having spent seven years in Europe, the United States and South America making gameshows and reality television.

"This has never been done anywhere in the world. It is exciting and has great potential," he raves.

Format television is here to stay, says Overett.

"It may move in and around the schedules, but publicly around the world it's an acceptable and extremely watchable form of television," he says from Avalon, where 100 Hours is being produced.

Overett describes 100 Hours as a gameshow where the viewers care about the contestants. "It is a cross between the entertainment value of The Krypton Factor with challenges and in the area of reality television, or observational television as well, a la Big Brother or Survivor, but with a reason to watch. We really give a full picture of each contestant."

Four contestants are locked in an underground bunker (the location is secret) with no timepieces and have to learn a series of challenges. They face off against the others until one of them wins and goes on to a final. The ultimate prize is a Mini Cooper.

There are three types of challenges: mind, body and dexterity and they range from walking on a high wire to building a lifesize triceratops skeleton.

It all happens over - yes - 100 hours: 50 hours learning the challenges, 20 hours sleeping, 30 hours down time. It's not sense-deprivation or water torture, says Overett, but the contestants quickly lose track of time.

"Within three hours, they'll be anywhere between one hour and six hours in what they think the time actually is."

There is also an element of strategising and bluffing, as contestants try to gain psychological advantage. Overett expects this element of the gameshow to ratchet up as new contestants know what to expect.

"I can't give the game away, but some contestants have said, 'Oh, I think I might throw the game', and then we've had them in the chatroom and they say, 'Yeah, I'm doing what I have to do to win'."

So who does want to be locked underground having to learn how to play soccer on stilts? Around 2000 people applied from all around the country, says Overett.

"We had a lot of people who were into extreme sports, a lot of physically fit people applied, and we also had people you would less expect, who have reached a certain stage in their life, even though they're quite young, where they want to try something different."

* 100 HOURS, TV2, Sunday 7.30pm