According to TechCrunch, NYC based Foursquare has just closed a $50 million round of funding. Their valuation: a whopping $600 million.

Boston based VC firm Spark Capital is a new investor in on the round, with Partner Bijan Sabet joining as a board observer. (As opposed to a full Board of Directors seat, board observers typically have no voting rights yet can still listen in on meetings.)

TechCrunch’s Sarah Lacy describes the round as being one of the most secretive rounds of venture capital the tech blog has ever witnessed. Mainly insiders were involved, including lead Andreessen Horowitz as well as previous investors Union Square Ventures and OATV. As mentioned, Boston’s Spark Capital joined as the most prominent new investor in on this round.

Rumors around this latest round of funding emerged in April when co-founder and CEO Dennis Crowley made a trip to Silicon Valley. At the time, rumors suggested he was looking to raise between $20M and $40M at a $500M valuation.

Crowley reports that Foursquare will use the money to build out its merchant platform, set up shop in San Francisco as well as continue to build out its international expansion. You can read the original announcement on the Foursquare blog. Having some fun, last night Crowley was celebrating at the Cannes festival. One of his tweets: