Reddit reviews City of Splendors: Waterdeep (Dungeons & Dragons d20 3.5 Fantasy Roleplaying, Forgotten Realms Supplement)

My recommendation would be to go pick up some 2nd, 3rd or 4th edition sourcebooks for dirt cheap at Half Price Books or online. The Forgotten Realms sourcebook from 3.5 is what I am currently using, it has a removable foldout map of Faerun, and detailed lists of major sights throughout the realms, including descriptions of the major cities, ruins, etc.

I've heard good things about the Greenwood Forgotten Realms book as well.

You can probably also find sourcebooks specific to Waterdeep, Neverwinter, etc. though I don't know the specific titles.

The point is that generally speaking the edition doesn't matter when it comes to background materials, physical descriptions, major characters, history, politics, factions, maps, etc. It just doesn't. So do yourself a favor and buy this stuff cheap from older editions.

Also, keep in mind that while you are building off of an existing world, and there is something cool about that, the minute you start to play in it it's YOUR world. None of these sourcebooks are going to have every single detail fleshed out, and often will just give you the flavor of a particular city, a few major landmarks, etc. From there on you should create your own landmarks, taverns, interesting characters, history, etc.

This is the book that I use a lot:
http://www.amazon.com/Forgotten-Campaign-Setting-Dungeons-Roleplaying/dp/0786918365/ref=sr_1_2?s=books&ie=UTF8&qid=1417478819&sr=1-2&keywords=FOrgotten+Realms

Here are more:

http://www.amazon.com/Greenwood-Presents-Elminsters-Forgotten-Realms/dp/0786960345

Neverwinter book:
http://www.amazon.com/Neverwinter-Campaign-Setting-Dungeons-Supplement/dp/0786958146/ref=sr_1_4?s=books&ie=UTF8&qid=1417478789&sr=1-4&keywords=Neverwinter+source+book

Waterdeep book:
http://www.amazon.com/City-Splendors-Waterdeep-Roleplaying-Supplement/dp/0786936932/ref=sr_1_1?s=books&ie=UTF8&qid=1417478895&sr=1-1&keywords=Waterdeep

http://www.amazon.com/Forgotten-Realms-Atlas-Karen-Fonstad/dp/0880388579/ref=sr_1_3?s=books&ie=UTF8&qid=1417478853&sr=1-3&keywords=FOrgotten+Realms

Hope that helps. Also buy 4th edition stuff now if you ever think you want it. Lots of stores are having fire sales moving their 4th ed stuff.

The book Forgotten Realms: City of Splendors has a lot of great info.

City of Splendors: Waterdeep (Dungeons & Dragons d20 3.5 Fantasy Roleplaying, Forgotten Realms Supplement)

https://www.amazon.com/dp/0786936932/ref=cm_sw_r_cp_apa_i_IEIIDbJWZB72H

I'm unfamiliar with 5th edition and any changes they have done to any campaign settings, so I might say something pretty stupid here.

So, why not go for something that has already been done in the FR setting? You could use the Undermountain, located under the mountain range (and the city of) Waterdeep. There is a 3.5 supplement of Waterdeep, and a 3.5 supplement for the Undermountain (and there is also one for 4th edition, but I have no experience with that one). The waterdeep book is mostly flavor, and you can use the undermountain book for the same reason and simply convert whatever you find interesting to suit your 5e needs.