It's a tearoom, in fact the Tajikistani pavilion from a long forgotten trade fair in Liepzig in the Soviet era, recreated inside a Berlin assembly rooms. You can be boring and sit at tables but better to recline on fat cushions at low tables and enjoy the range of exotic teas.
Am Festungraben 1, right behind the Neue Wache on Unter den Linden, in a building that houses arts organisation admin offices and meeting rooms.
www.berlin-hidden-places.de/yuba_web3/sachindex_en/cafe-/mit_tadshik_en.htm