What is one official residence of the monarch located outside of England?

The Palace of Holyroodhouse is indeed an official residence of the monarch located outside of England, specifically in Edinburgh, Scotland. This royal palace serves as the Queen's official residence in Scotland and is used for various state ceremonies and official engagements. Its historical significance and role as a residence on Scottish soil make it distinct among the choices.

In contrast, Buckingham Palace, Windsor Castle, and Sandringham House are all located within England. Buckingham Palace serves as the official London residence, Windsor Castle is situated in Berkshire and is the oldest and largest inhabited castle in the world, and Sandringham House, located in Norfolk, is a private residence of the monarch. While all these locations hold importance for the British monarchy, only the Palace of Holyroodhouse fulfills the criterion of being outside of England.