I'm not much of a bar person, but a few stand out in my pre-Covid travels:

The Library Bar - Saint James Paris
La Magritte Bar (plus the private, residents only Cub Room which I don't think exists any more) - The Beaumont, London

Honourable Mention to: Lewers Lounge - Halekulani, Honolulu (The bar itself is not very special from a global perspective, but a space like that is hard to find on Oahu)