Only being described with either a symbol or a warning, Desolation was the closest thing to a name borne by a planet in the Twelve Galaxies. It was located in a trinary star system and had three moons. The planetary environment featured mountains, mist swamps, and acetylene fields.
The planet was colonised in ancient times. These first settlers witnessed a mysterious structure that phased into existence every thousand rotations, which they called the "Ghost Monument". This was actually the Doctor's TARDIS, whose engines had become stuck in a loop due to damage caused by the Twelfth Doctor's regeneration. The TARDIS used this time to rebuild and wait for the Doctor to recover it.
Some time later, the planet was conquered by the Stenza. They kidnapped a group of scientists and extorted them to create new means of destruction, including weapons, poisons, and deadly creatures. The planet was used as their testing ground. The scientists were held in a maze of underground tunnels that spanned half the planet.
Eventually the planet's ecosystem was completely destroyed and its inhabitants eradicated. It was said that the planet had been "made cruel": the atmosphere became toxic, the water was filled with flesh-eating microbes, and killing machines and creatures such as the Remnants and the SniperBots infested the surface.
The surface of the planet became even more dangerous at night as the Remnants would move openly while remaining dormant during the day.
The planet itself fell out of its orbit. The captive scientists attempted to destroy their research before the Stenza could use it against anyone else.
Desolation was used as the final stage of the Rally of the Twelve Galaxies. During this event, the Thirteenth Doctor, Graham O'Brien, Ryan Sinclair and Yasmin Khan visited the planet to search for the TARDIS. With help from the Doctor and her companions, the two finalists, Angstrom and Epzo, both won the race and were teleported away from the planet by Ilin. The Doctor was able to stabilise her TARDIS and escape Desolation. (TV: The Ghost Monument)