The universe known as N-Space, despite its infinite diameter, possessed a centre.
Located there was the planet Villengard. (TV: The Doctor Dances, Twice Upon a Time)
The space station Terminus was reported to be in the exact centre of the universe. (TV: Terminus)
Having assembled the Key to Time, the Fifth Doctor took it to the centre of the universe, where it was used to initiate the Second Age of Time. (GAME: The First Adventure)