Lena Dunham guest stars as "Betty" on the 48th epidsode of a tv series set in what post apocalyptic land? 
Betty (Adventure Time): "Betty" is the forty-eighth episode of the fifth season of the American animated television series "Adventure Time". Betty (Adventure Time):  The episode guest-stars Lena Dunham as the eponymous character, Betty. Adventure Time (season 5):  Finn and Jake live in the post-apocalyptic Land of Ooo, where they interact with the other main characters of the show: Princess Bubblegum, The Ice King, Marceline the Vampire Queen, Lumpy Space Princess, BMO, and Flame Princess.
Land of Ooo