A palace was a residence for royalty.
The Citadel of Peladon was the palace that served as the seat for the Royal House of Peladon. The Doctor visited it on every occasion that he was on Peladon. (TV: The Curse of Peladon, The Monster of Peladon)
Buckingham Palace was the London home and primary residence of the British monarchy. In 1889, Li H'sen Chang was scheduled to perform for Queen Victoria at Buckingham Palace but he was killed one month earlier. (TV: The Talons of Weng-Chiang) The palace was destroyed in the 22nd century Dalek invasion. (PROSE: Legacy of the Daleks)