WATERDEEP: CITY SYSTEM MAP SET (Forgotten Realms)
I consider the Forgotten Realms City System set (Amazon link) to be an underappreciated gem. It’s difficult to grasp the size this map set. Here’s a photo of me with the 10 maps of Waterdeep put together.
The set also has (not shown here) a smaller overall map of the city, a 32-page guidebook, and a poster with an artist’s rendering: An aerial view of the city.