Tomb of Valdemar
Ashkellia was an artificial planet.
It was the second planet in its system, orbiting a minor star at a distance of eighty-nine-million miles in a sparsely clustered area of Mutter’s Spiral. It had an atmosphere with sulphuric acid clouds and an average surface temperature above six hundred degrees Celsius.
Ashkellia was in fact a giant particle accelerator built over a million years before the Fourth Doctor and Romana visited there. The Palace of the Old Ones was the control centre. It was used to explore the higher dimensions. (Tomb of Valdemar)