The Carpanthan city was home to the Carpanthans.
The original city was accidentally destroyed by a depth charge. To rebuild it, the Carpanthans hijacked the Monitor to send out false messages to ships and sink them. The shipwrecks then were moved, forming the basis of the new city with streets and parks. The city also had breathable oxygen. When the Third Doctor and Liz Shaw went down to investigate the ships' disappearances they were charged and found guilty of the destroying the city. The Doctor managed to convince them them that he would not reveal the species' existence so the judge decided to let them go, with the request they visit again in the future. (COMIC: The Fishmen of Carpantha)