Back in the late 1800s New York City was rich in biergartens, some legendarily enormous. They were primarily built for, and by, the city's burgeoning German population. But then Prohibition in the 1920s and an anti-German sentiment inflamed by two world wars threatened the city's biergartens with extinction.
Luckily, in just the last few years, the city has undergone a beer gardenwiedergeburt (rebirth). They are bubbling up on building rooftops, under train overpasses and in repurposed auto garages. ... According to Beer Gardens NYC, a new mobile app whose very existence is an indicator of the resurgence, there are more than 50 spots currently meeting the app's (rather loose) definition.
I've been to a few of the ones mentioned, and they're quite nice.