The Titan Zoo was a zoo on Titan at some point in the mid-to-late 22nd century, once visited frequently by the boys from the Dwarf.
Dave Lister once used a photograph of Arnold Rimmer's mother as an ashtray, claiming he believed it to be a "souvenir from Titan Zoo." (Me²) On another earlier occasion, whilst on planetary shore leave on Titan, Lister and Rimmer were chatting up "two brunettes from supplies". Rimmer suggested that they all go visit the Titan Zoo, to which Lister replied that Rimmer meant he "wanted to take them home to meet his mother already". (Kryten)