The Bar/Lounge at Generator Berlin Mitte
Generator Berlin Mitte's bar/lounge is endorsed by professional travelers. Of the 4 publications tracked on TripExpert, 2 recommended the bar/lounge, including Time Out and Oyster.
Generator Berlin Mitte 
Time Out
Oyster
Time Out "It’s definitely geared towards a younger crowd, with urban art on the walls and a late-night bar with DJs on weekends"
Oyster "There's another Generator hostel in Berlin, Generator Hostel Berlin Prenzlauer Berg, which is farther from the city center, but offers an outdoor barbecue area in the summer and free parking"
