Part of the fun of RPG adventure writing, for me at least, is the act of creating something from nothing. Spinning a saga whole-cloth from the old Grey Room is a fine art, and when the process works and you can sit back and examine what you’ve created and … well, it’s great. Sort of like enjoying a gourmet meal you spent all day cooking, to use an easy culinary analogy.
Trouble is, our brains often follow a similar track. Not mine to yours, but mine to mine. If I create one dungeon, I’ve got to be careful to make the next one different, and so on. It’s easy to get into a mental rut. If I design a underwater sahuagin palace with the same standard outer guard rooms as my last orc cave complex, what’s the point? They might as well all be orc complexes.
Some RPG authors are good at keeping things fresh. Gary Gygax wrote three giant lair modules and each one presented a unique giant lair. That's adventure writing. But for most of us, it's more of a challenge to keep things fresh.
I’ve finally come to realize that using the real world for inspiration isn’t a bad thing. Our real world is loaded with inspiration. So is our media. Seen a good movie lately? Have a favorite old Star Trek episode? Remember a creepy gothic story? (Go H. P. Lovecraft! Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!) Hear about some political machinations on public radio? Read about a devious murderer finally brought to justice? It’s all good fodder for the mill. Sometimes the mere act of watching a fantasy movie—even a cheesy one—is enough to jump-start my mental engine. Take ideas when they appear and run far with them.
Real world cultures are also a fantastic inspiration. The other day I watched a dog show on television and I was boggled as to the sheer number of breeds of every size and shape out there (and yes, I know man custom breed many of them, don’t spoil my fun). In a similar fashion, the range of cultures that have inhabited our planet blows my mind. Eskimos, Viking warriors, samurai, Hopi Indian, Aztec, … it goes on and on. All these cultures have art, homesteads, rituals, clothing, religion, ways of war, methods of surviving, etc., all unique to them. Compare ancient Japanese armor to Middle Age European armor—very different, yet both fairly effective for their time. All armor doesn't have to be the same. And all dungeons need not be the same either.
Currently I’m working on a potential project and I’m using the Anasazi, Mayan, Aztec, and American Indian (Sioux and Chippewa /Ojibwa tribes, and others) as inspiration in developing several humanoid cultures and customs. Does this mean my humanoids believe in Thunderbirds or Huitzilopochtli? Not quite. But perhaps my humanoid tribe leaves petraglyphs on rock walls. Perhaps they sacrifice prisoners to their god. Maybe they even play a primitive ball game, not unlike pitz.
When I envision weird temples or ruins, I might think of Tulum or Stonehenge, or when I create a castle, I might think of Cardiff Castle; to name three real-life places that I was able to visit in person that later had a direct effect on my writing. My current ruin-muse is Angkor Wat (haven't gotten there yet, unfortunately).
The idea is to draw upon the basic ideas, the things that make you interested, and make them your own. Soon all your dungeons won't look the same anymore, and your readers and players will thank you for it.