The Dungeons & Dragons city of Waterdeep on the Sword Coast is a solid favourite of mine. When Waterdeep: Dragon Heist was released, I delved into the book and ended up with two groups to GM for.
For one of them, I ran the adventure essentially ‘by-the-book’. At least for the first session. I love expanding on settings and storylines when I GM, customising things to the players and creating new NPCs and storylets for them to consider.

The other group got a heavily customised version of the campaign- locations, NPCs, story paths, items… And it was great to be able to write custom things for my friends and players to make it more meaningful to them.

Though the campaign never saw its end (I lost my confidence as a GM for a while), I have been slowly re-working things and converting it to a possible Pathfinder 2 system setting.