The design for the 2012 Olympic stadium, based on a sunken bowl, was unveiled today.
Olympic organising committee chairman Lord Coe described it as a "stadium for a completely new era that will be inspiring and have a lasting legacy".
It has 25,000 permanent seats sunken into the bottom, with a layer of 55,000 temporary seats above and a roof that will cover two-thirds of all spectators.
Outside the stadium will be pods filled with facilities for spectators, such as food stalls.
Key to the design of the £496 million venue in Stratford, east London, is that it must shrink from an 80,000-seat capacity venue during the Games to one of 25,000 seats afterwards.
It will then become a multipurpose venue used for athletics and other sporting and community events, but no anchor tenant has yet been found.
Original cost estimates did not include VAT and inflation.
John Armitt, chair of the Olympic Delivery Authority, said: "Nearly £500 million is a lot of money in anyone's terms but it is the budget and we are determined to work within that.
"If there is a requirement for any extra, we have a contingency within the scheme covering this as a whole and we will use some of that, but that is not the plan."
The stadium build is being led by construction firm Sir Robert McAlpine Ltd in a partnership including architect HoK Sport and consulting engineer Buro Happold.
Building work is set to begin up to three months ahead of schedule in April or May, with completion in 2011 to allow for test events.
The venue is being built on land dubbed by the designers as Stadium Island, as three sides of it are surrounded by water.
The Olympic Flame will probably be on the northern end of the Island and outside the stadium, but talks are still under way about its final siting.
Most of the stadium building will have a shelf life of one or two years, so the designers have created a fabric wrap around it using graphic colours, mosaics and Olympic-related images that can change.
Talks have begun with a firm which can turn this fabric into bags which can be sold after the Games. The temporary seats are also set to be sold.
With the eyes of the world on London in 2012, getting the stadium wrong is something the organisers cannot afford. They have been keenly aware of criticism that it could turn into a white elephant and get little use after the games.
Finding a post-games tenant is important. West Ham were tipped as a possible, but the idea of them or any other Premiership club moving in has now been ruled out.
London mayor Ken Livingstone said: "It is really inconceivable that anyone would have signed up to occupy a stadium before they could see it.
"Now that we have this design, I think we will move very rapidly on negotiations for people to come in and sign up for the ongoing legacy use."
He said the stadium design "must be the most environmentally sustainable stadium ever constructed anywhere on the face of the planet".
But one black mark against the grand unveiling in the Olympic Park was that invited guests using the Jubilee Tube line, which serves the venue, were held up because of long signalling delays.
Mr Livingstone explained that a new signalling system has been ordered, and pledged that the Jubilee line signalling system will have "a good two years of practice" having to cope with the crowds for the Olympics.
Details of the transition for the stadium after the Games are to be announced in the next few months.
Rod Sheard, senior principal at Team Stadium, which is leading the stadium construction, said that "as many of the 25,000 seats, if not all" will be covered.
Asked if the temporary design had increased costs, he said: "These are expensive buildings - it's true.
"Whether it is more expensive to build than a permanent... it probably would be, but there are benefits which are huge."
Mr Armitt added: "It would be very different, very traditional and be nowhere near as exciting (without the temporary element).
"Today we have three solutions - a solution for the Games, a solution for legacy and a kit of parts which allows us the opportunity to do something else for the UK. So essentially, you get three for the price of one."
Olympics Minister Tessa Jowell said this complements the other stadiums in London - Wembley, Emirates and Twickenham - and speaks very directly to the International Olympic Committee for a new kind of Olympic development, one that focuses very much on legacy and long-term sustainability."