I want to share with you my favorite map of all time.
It's a map of the Fuqua School of Business (no, really, that's its name, pronounced FOO-kwa) at Duke University, that I obtained as a student in the late 80s. I worked in the IT department at Fuqua, backing up hard drives on to large tape cassettes and had to visit every office in the place.
Check out the notes on it. Things like "Gas Impermeable Force Screen" and "Huntsman Lift Tube" and "Used As the Knowles Institute". I can assure you that none of these things are true. It is a business school with no huntsmen in sight, but in one of the games I ran, huntsmen were the enforcers of the Big Bad who made his headquarters in a building like this. I even paced out the dimensions of the place and wrote in the scale on the map.
There's only so many good ideas out there, and you know it's true. How many times have you seen a movie and thought, "This is just like Conan The Barbarian meets Star Wars"? (Okay, probably not that often, now that I think about it, but something like that.) It's a Hollywood truism that movies are pitched this way, by taking two ideas that have already been done, and combining them--recycling them into a new story.
In an RPG, there's no reason why you can't do the same thing. After 30+ years of gaming I've created all kinds of adventures, settings, characters, maps, and whatnot, and coming up with something brand new that I've never done before, and I figure "Why bother?" What was cool for one group of players could be cool for another, so why not re-use interesting maps, locations, or NPCs after adapting them for the current campaign?
Over the years, that map has been pressed into service as a mental hospital, a prison, a research institute with sinister plans, and even a moon base. I have photocopied it a hundred times, then cut it up and pasted it (literally; this was before scanning was a commonplace) onto graph paper in different permutations. I added floors where there were none, installed secret passageways and high-tech defense systems, and populated it with vicious, gun-toting guards. It has been the center of Illuminati campaigns, Traveller campaigns, Psionics and Supers and Firefly and Wars Against the Robots campaigns.
The Fuqua School of Business doesn't look much like I remember it, but who cares? The old map still serves me well. Go back through your old adventures and notes. Find some cool stuff that you could recycle into your latest campaign, polish it up, and plug it in.
