The Corinthia Hotel, London, opened in 1885 as the Hôtel Métropole until 1936 when it was taken over by the Ministry of Defence, later reopening as a Corinthia Hotel in 2011.

During the war, the building was used as the headquarters for MI9, a significant government organisation which coordinated and executed a large number of prisoner of war escapes across Europe. It is also believed that room 801 in the building held the government's records of UFO sightings

Churchill wrote of hearing Big Ben strike on Armistice Day, as he watched from a window as hundreds of Londoners poured onto the streets in celebration.

Sauce:

https://www.dailymail.co.uk/travel/travel_news/article-3336602/An-ancient-thermal-grotto-hidden-Masonic-temple-forgotten-air-raid-shelter-secrets-world-s-oldest-hotels-revealed.html