After years of delays and running millions of pounds over budget, the Bath Spa is to open to the public.
The hot springs produce 1.2 million litres of water a day
It is estimated the Spa with its mineral-enriched waters will bring in around £20m of business to the city every year.
"I feel it's very important for the economy of Bath," said Theresa McDermott, Bath Chamber of Commerce.
In order to break-even on running costs, the Spa will need to attract around 250 people each day.
"It's the only hot spring in the UK and as such it will have world-wide recognition just the same as the spas in Germany or Hungary and I feel it will be a very big attraction for people coming from overseas to enjoy the facilities," Theresa McDermott added.
People living in Bath and North East Somerset will get a 15% reduction on entry but could get in for free in the future.
The councillor responsible for the Spa, Nichole O'Flaherty, has said it would cost the authority £2.5m a year and that if enough people wanted it, it could be arranged.
For the past 20 or so years the springs - which produce some 1.2 million litres of hot water every day - have been closed to the public.
They were closed in 1978 amid fears over the safety of the water source after a woman died of Legionnaires' Disease.
In the intervening years, five attempts were made to rejuvenate and reopen the thermal waters to the public but each eventually failed, until the city hit upon the idea of doing so as a millennium project.
But the project was beset with problems as costs rocketed and squabbles broke out between the authority and the builders, Mowlem.
The grand opening will be the first time people in the city - which takes its name from the hot waters - will be able to look around the new facility.