What is the official designation of the building visible from the Morpeth Arms in a manner enabling spying?
SIS Building The SIS Building or MI6 Building at Vauxhall Cross houses the headquarters of the Secret Intelligence Service (SIS, MI6), the United Kingdom's foreign intelligence agency. It is located at 85 Albert Embankment in Vauxhall, a south western part of central London, on the bank of the River Thames beside Vauxhall Bridge. The building has been the headquarters of the SIS since 1994.
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.