Ruins are awesome. We’re all in agreement, right? We go tourist on them (at least, until some fool starts vandalizing the plinths or screwing under the altars or attempting to Life Imitates Action Movie through them, and then we can only admire them from a distance, not that it keeps us from trying), we write about them, we study the socks off of them, we sneak them into our game sessions—heck, I have seen full books, and full gaming supplements, that hit a ruin and exhaust themselves in it. So what’s so cool about them?
They’re good for exploration. Your average fictional ruin is large enough to get lost in or to require a Designated Mapper for—just the size that would make a good dungeon-crawl—and yet self-contained; there’s a definite border to it, so you know you don’t have too big a risk of someone going off in the other direction and never realizing it, unless it magically Does That. It’s alien enough to be worth poking, what with being a remnant of a fictional society, but familiar enough to be comprehensible. Mostly.
They look cool. After all, anything that’s lasted this long while abandoned and slowly being worn away has to have been built to last, and big enough that it’s still recognizably a Relic of Ancient Times rather than just an interesting-looking rock formation. Big is nifty, and if something’s built to last it’s likelier to be built to look good than something that isn’t, since the people who can afford the expensive materials from far away are also the ones who can afford the frescoes and the mosaics and the carvings of their exploits running all around the walls. Then you have the Ancient Technology Civilizations, who add to this being able to do improbable things with the architecture, and—instant jaw-dropping, just add pretty prose or images.
It’s easy to adjust to the level of the characters experiencing it, particularly to adjust downward. A ruin is a mystery in and of itself—who were these people? Why did they go away? What probably-relevant legend are we going to find hints of in here? The whole complex is a one-sided conversation with a dead civilization just waiting to happen! As a result, you don’t even need hostile occupants to make it interesting. And if you are the type for traps and semi-regular combat encounters, the ruin can still limit what it makes sense to have in there; you aren’t going to get a monster that doesn’t fit inside, after all.
They have an amazing range of emotional resonance. Even before you get into the clear signs of the former occupants, there’s awe and wonder, from the look of the place and the question of how it was built (extra credit if the ancient race didn’t have magic at their backs, just a better understanding of physics than we would ordinarily give them credit for), and the pathos of a great civilization that is now no more. Then you get into whatever motivations the characters have tied into finding the place (or the surprise of tripping over it), and how they feel about what they can gather of the culture, and (where applicable) the frustrations over its pitfalls and pride over surmounting them, and more. One-note locations? Not so much.
Now excuse me, please—I have some ruins to help design!