Social gaming firm Kabam said today it has signed a multi-year lease on a “spectacular” new office in downtown San Francisco. The move shows that the city is ground zero for the social game industry.

Kabam‘s 450 employees will now work together in a 63,000-square-feet office next to the Moscone convention center in the same space that currently houses Twitter.

Kabam, the maker of hardcore social games like The Godfather: Five Families, joins other social gaming companies such as Zynga, EA-Playfish, Disney-Playdom, 6waves Lolapps and others in setting up in San Francisco, where Kabam already had a smaller office.

The new headquarters is at 795 Folsom St. Kevin Chou, chief executive, said the move will maximize cross-team collaboration and prepare the company for its next phase of growth. Terms of the lease were not disclosed.

Kabam recently acquired the independent game studio Fears Studios, adding six employees.

Kabam has raised $125 million — a huge amount of money for a social game publisher — and now it has begun to spend it.

Kabam was founded in 2007 as Watercooler and funded by Betfair and Canaan Partners. It had around 20 employees for quite a while as it experimented on Facebook, making sports fan pages and sports games. It had a big hit with its first major role-playing game, Kingdoms of Camelot, which quickly pulled in millions of users. The game still has 1.5 million monthly active users 19 months after its launch. Kabam also acquired WonderHill, a San Francisco game company that developed Dragons of Atlantis, which has become Kabam’s most successful game to date.

The company has raised multiple rounds to date.