What is the official designation of the building visible from the Morpeth Arms in a manner enabling spying?
Morpeth Arms The Morpeth Arms is a public house at 58 Millbank, in the Pimlico district of London. It was built in 1845 to refresh prison warders serving at the Millbank Penitentiary. It now contains a Spying Room which provides a good view of the headquarters of the Secret Intelligence Service across the river. The building is listed as Grade II and it is now part of the Young's estate.
Sally port A sally port is a secure, controlled entryway to a fortification or prison. The entrance is usually protected by some means, such as a fixed wall on the outside, parallel to the door—which must be circumvented to enter and prevents direct enemy fire from a distance. It may include two sets of doors that can be barred independently to further delay enemy penetration.