Europe's biggest casino and conference centre is coming to Spain later this year, creating thousands of jobs.
But angry protesters claim it will bring with it problems of gambling addiction and prostitution.
The building of EuroVegas, a sprawling complex of hotels, casinos and conference centres is set to emerge from the small town of Alcorcón, just outside Madrid.
Multibillionaire Sheldon Adelson's Las Vegas Sands corporation announced that initial funds of £8.3 billion were in place to start work on the 36,000-hotel-room resort, which may also be home to a replica of New York's Times Square.
Adelson is the 14th richest person in the world, and was a key backer of the failed Republican bid for the US presidency by Mitt Romney.
There have been questions on where the money will come from to fund such an expensive project. Las Vegas Sands will provide 35-40 percent of the funding, but the source for the remaining 60-65 percent is unclear.
Michael Leven, Adelsen's number two, said Spanish banks would be among the investors, but declined to name them.
Spanish daily El País has estimated that around 40,000 employees will be needed in the first phase, with final figures of up to 250,000 direct and indirect jobs estimated - which would halve unemployment in the Madrid region.
"We are building four resorts in the first phase, with approximately 3,000 bedrooms in each resort and the attendant facilities," said Michael Leven, Adelsen's number two.
"Singapore, which is about the same size as one of these [12 eventual resorts], employs approximately 10,000 people directly and 10,000 more indirectly."
According to the Guardian, there have been years of negotiations over the gambling complex. Madrid's regional president Ignacio Gonzalez virtually promised that Spain's central government would deliver the tax changes, infrastructure as well as the controversial exemptions to the no-smoking laws requested by Adelson.
"The smoking issue is also a matter for central government. It is working on it and will come up with a solution in the next few months, with a chance for restricted smoking," said Gonzalez.
Protesters claim that the government was creating a special low-tax "mini-state" for Adelson in the EuroVegas complex.
Alcorcón's mayor, David Pérez, said that the project, which is expected to cost a total of £18 billion, will turn his town - which has 15,000 jobless among its 170,000 inhabitants - into "an unprecedented nexus of employment just at the moment that it is most needed".
The EuroVegas No platform group said in a statement: "The most probable thing is that EuroVegas provides profits for a very few while causing irreversible environmental damage."
Gonzalez hit back, saying: "This project is not just about gambling, but is an integral resort."
Over one million visitors are expected to come to EuroVegas from all over the continent.
Work on the first of the three phases starts at the end of 2013 and is expected to end by 2023.
The resort, which is equivalent in size to 750 football fields, will comprise 12 hotels, six casinos, a convention centre, three golf courses, theatres, shopping malls, bars and restaurants.