So here's a question for you worldbuilders: Do you have a subscription to National Geographic?
Regardless of what kind of worldbuilding you do, odds are there will be articles in National Geographic that will be useful or interesting to you. Frankly, I don't know of a single resource out there that would be better for compiling together the kind of fascinating cultural, biological, geological and historical information that any worldbuilder would want to get their hands on. Every issue is chock full of ideas you can use.
Paris Underground: This one was so critical. Maradaine is an old city, with lots of underground sewers, catacombs and forgotten tunnels. The article helped me clarify depths, usage, and practicality.
Angkor: The ancient city, then and now. A good encapsulated look at a non-Western culture's ancient style and engineering.
Incas: Another great look at a historical culture.
Plus, EVERY MAP YOU COULD EVER WANT.
Next time, we'll talk more about food. And maps.