Plazas, atriums, terraces, and small parks, all built by capitalists, all for the people — and all thanks to the 1985 Downtown Plan. These little gems remain a mystery to many in San Francisco, yet like any great surprise, they've been right there the entire time. Popular by day mostly because of their concentration in the lunch-crowd heavy FiDi-SoMa corridor, they're virtually deserted by night. Another little secret is that a lot of them are open 24 hours a day, unlike almost every other park in the city. So when business hours are over, it can still very much be business time in the privately owned public open spaces, or POPOS, of SF. Next time you're downtown late — we won't ask why — stumble on over to 50 Beale St. Not only is this POPOS loaded with flora and seating space, it has a museum in the form of a replica Bechtel Corp private railcar. It will be closed, but you can peer in through the windows, shimmying along the landscaping imagining yourself a stowaway on a sluggish coach heading toward the golden West while balancing a can of beer or joint in one hand, all while surreptitiously avoiding the sometimes watchful eye of building security.