You may be looking for the planet Avalon.
Avalon was an alternate dimension created by Gallifreyan Interventionists. It existed in the unconscious mind of King Constantine, whose dreaming gave it substance. It was made for the Catuvelauni, a Celtic tribe, to escape Roman invaders. Also living in Avalon were the Fair Folk, Silurians who were unintentionally brought along with the Catuveluani.

The TARDIS hit a weak spot in 2012 between Avalon and England, causing its apparent destruction. The collision opened a rift between the dimensions. Before the rift was sealed, Avalon was where Compassion completed her transformation into a TARDIS. (PROSE: The Shadows of Avalon)

Ancelyn and Winifred Bambera once went on a holiday to in Avalon. (PROSE: Faithful Friends: Part 3)

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