Waypoint

Space-time Waypoints were points in time and space that became supercharged with vortex energy.

During a temporal crisis which grounded TARDISes and similar machines throughout the universe, the Doctors realised they could only travel from one Waypoint to the next, draining each of vortex energy to temporarily, messily re-power their TARDIS before depleting their reserves with the next hop.

These Waypoints included UNIT HQ, which became charged with vortex energy due to "almost passing through the event horizon of a black hole" (GAME: Lost in Time) when Omega transported it to his anti-matter universe, (TV: The Three Doctors) Atlantis (frozen in its final moments in a time eddy) because of the Crystal of Kronos, the Dalek City on Skaro at a early point in its history that future Daleks had visited, the Panopticon on Gallifrey, the place in Nevada where Clara Oswald parted ways with the Twelfth Doctor, the Underhenge right before the Eleventh Doctor was placed in the Pandorica, and the Minyan spaceship. (GAME: Lost in Time)