Gardezza was a planet covered entirely by the Viscoid, within which the native Gardezzans lived. It was once visited by the Doctor and was home to the Master's damaged TARDIS for five centuries after the Daleks forcibly transmatted him out of it.
The planet was invaded and occupied by the Daleks during the Last Great Time War, destroying the capital city and forcing the Gardezzans to flee to various seabed bases. The Master visited the planet in an escape capsule in search of his TARDIS and agreed to assist Nius and her rebels against their oppressors, eventually leaving in his TARDIS and destroying the Dalek command ship. (AUDIO: Beneath the Viscoid)