Elystria was a planet visited by the Doctor twice. It was the homeworld of the Elystrians. The Doctor visited the planet at its peak. It was known as the Planet of Paradise due to its perfect and peaceful society.
The Fourth Doctor visited some three hundred fifty Elystrian years later to find the landscape drastically changed after the downfall of the Elystrian society. This was the result of Vayla's robots overthrowing their masters. The robots were eventually deactivated and Vayla was restored as leader. (PROSE: Planet of Paradise)