Four environmental groups are competing for £50 million of lottery money, the largest single amount ever awarded by the Big Lottery Fund.
Following a public vote which closed on 10 December, an announcement is due on who has won - the Eden Project, sustainable transport charity Sustrans, the Sherwood Forest Living Legends or the Black Country Urban Park.
THE EDEN PROJECT - THE EDGE
Author Philip Pullman will be one of the designers
The Eden Project creators have big ideas of how the £50m grant could take their multi-award winning attraction to another level.
If it were to scoop the £50m, the Edge project would explore what it is to be human and why past civilisations have collapsed, Eden's chief executive Tim Smit said.
Inside a three-level building there would be a vast oasis dedicated to arid climate - or "Blade Runner territory" - and beneath would be chambers with displays whose designers will include musician Peter Gabriel and children's author Philip Pullman.
One of the chambers would be built out of loud speakers. Audio recordings in every one of the earth's languages on the subject of love would be played simultaneously. The point, says Mr Smit, is to create a human song.
The Eden Project, a so-called living theatre of plants and people, in St Austell in Cornwall, has attracted nine million visitors since opening in 2001.
Mr Smit said winning the prize would be "the most fantastic accolade", as it would be chosen by the general public.
"To have the privilege of creating a building we believe could be among the most important ever built would be humbling, scary and massively exciting," he added.
SUSTRANS - CONNECT2
New routes will help to reconnect communities
The Connect2 project promises to change the way people travel in 79 communities across the whole of the UK.
By building footpaths, cycle paths and bridges, transport charity Sustrans wants to get people out of their cars and on their feet or into the saddle.
About six million people live within one mile of one of the projects.
The communities chosen - including areas in Cardiff, Bermondsey, south-east London, and Sleaford in Lincolnshire - are all severed in some way, whether by a river or too few cycle routes.
Sustrans Chief Executive John Grimshaw said he was "excited, but on edge" as he waited for the result.
"There are a lot of communities and groups who are relying on our success," he said.
The project could also help create a fitter, healthier population and let individuals make a difference to the problems of climate change, he added.
"If we don't get it, it would be a huge disappointment to a large number of people," he insists.
"We've had the most amazing support from a very wide range of groups right across the country."
The total project costs £147m with funding coming from a range of sources.
SHERWOOD FOREST: THE LIVING LEGEND
Sherwood Forest has seen visitor numbers fall
You would think the home of Robin Hood would have a much bigger pull than it does.
But currently just 400,000 people visit Sherwood Forest each year.
But the Living Legend project is aiming to turn around its fortunes and more than double visitor numbers in the first three years.
Organisers hope that through a combination of audio trails, sculptures and parks they can attract one million visitors each year.
The project will also include a new visitor centre with a viewing platform created from steel and wood in the shape of a tree and 95km of new cycling and walking routes.
Returning the forest to the Sherwood of old will involve replanting hundreds of trees that were chopped down over the last 100 years and never replaced.
Austin Brady, chair of the project's board, said that tonight was a "once in a lifetime opportunity" which he did not want to pass up.
He said: "This is the best chance we will ever have to give Sherwood Forest the recognition and investment that it richly deserves."
BLACK COUNTRY URBAN PARK
The project aims to bring economic prosperity to the region
This project aims to reveal the area's hidden gems.
Taking in Wolverhampton, Dudley, Walsall and Sandwell, the region suffers from poverty and negative perceptions, according project leader Sarah Middleton.
But a 30-year plan aims to lift the population of one million out of that through regeneration, using its industrial heritage to drive the transformation.
Limestone caverns which were dug out to create canals will be made safe and accessible, waterways will be transformed, and green spaces will be introduced.
Ms Middleton, chief executive of the Black Country Consortium, said the changes should bring business to the area, and therefore economic prosperity.
The Fund offered the opportunity to "turn the Black Country 'green'", she said.
She also hoped the caverns in Dudley will attract 80,000 more visitors to the Black Country.
The entire cost of the project overall is £106m.