Tromesis was a city that the Second Doctor, Zoe Heriot and Jamie McCrimmon visited. It had very large buildings and Jamie couldn't see the sky. It was built in what was once Switzerland during the First World Flood. The Second World Flood was far worse and devastated much of Earth, leaving Tromesis as the last inhabited city on Earth, with a population of approximately four million. The Second Doctor described it as being, effectively, the capital of Earth. (AUDIO: The Apocalypse Mirror)