Tromesis
Tromesis was a city located in what was once Switzerland. It was bulit duing the First World Flood. Some time later, the worse Second World Flood devastated much of Earth, leaving Tromesis as the last inhabited city on Earth. A device called the sympathy engine was used to create a better city, but resulted in two cities coexisting in the same position in the Universe, but out of phase.
When the Second Doctor, Zoe Heriot and Jamie McCrimmon visited the city, each of the destitute and "better" cities had 4 million people. It had very large buildings which obscured the sky. The The Second Doctor described it as being, effectively, the capital of Earth. They helped to migrate people to the better city, doubling its population. (AUDIO: The Apocalypse Mirror)
