The Banqueting Hall, later the Chapel Royal, is a 1622 hall on Whitehall in Westminster and a database landmark in Syndicate. It is the only surviving part of the old Palace of Whitehall.
It hosted royal receptions and performances, and Charles I was executed in front of it in 1649. When the rest of the palace burned in 1698 it became the new Chapel Royal; Queen Victoria turned it into a museum in 1891.
In 1868 the building is still serving as the Chapel Royal; its database image is even filed under that name. You find it on Whitehall in Westminster, close to Horse Guards.
10 Downing Street
10 Downing Street is the Prime Minister's home and office in Westminster. In 1868 Benjamin Disraeli lives here, and Jacob's work as his bodyguard in Sequence 7 starts outside the house.
Admiralty
The Admiralty is a government office on Whitehall in Westminster, one of the period buildings you can climb and read about in the in-game database. No memory centres on it.
Blue Anchor Alley
Blue Anchor Alley is a Blighter stronghold in Westminster run under Lilla Graves, one of two in that borough. Freeing it lets the Rooks set up there instead.
Buckingham Palace
Buckingham Palace is Queen Victoria's London home in Westminster and the setting for the climax of Syndicate's story, the Queen's ball. It is also where the Queen hands out the Operation side memories, and it has a viewpoint.