Buckingham Palace:

At the centre of this wing is the famous balcony with the Centre Room behind its glass doors. This is a Chinese-style saloon enhanced by Queen Mary, who, working with the designer Sir Charles Allom, created a more "binding" Chinese theme in the late 1920s, although the lacquer doors were brought from Brighton in 1873. Running the length of the piano nobile of the east wing is the great gallery, modestly known as the Principal Corridor, which runs the length of the eastern side of the quadrangle. It has mirrored doors, and mirrored cross walls reflecting porcelain pagodas and other oriental furniture from Brighton. The Chinese Luncheon Room and Yellow Drawing Room are situated at each end of this gallery, with the Centre Room obviously placed in the centre.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". The Principle Corridor features which type of doors?
mirrored doors