When I sketch out some ruins from scratch, they don't always feel ruin-y enough for me. We're talking about proper ruins here: wrecked castles, burn-out ghost towns, Scooby Doo haunted mansions, etc. So I thought I'd try thinking about a better procedure than treating the ruins as an above ground dungeon. Here's what I've got so far.
I - Begin with Theft
Dig through free online adventures and/or your personal pile of game crap and find one of those bright shiny home base areas. The titular Keep on the Borderlands or Village of Hommlet, to give a couple examples. To build your ruins, you're going to assume that these places as written exist in your campaign's past.
II - Figure Out Who or What To Blame
You need to figure out why the original locals moved out. Look over the notes for your campaign history. Any really good catastrophes or epic wars you can tie your ruins to? Did this place succumb to the Rain of Colorless Fire? Did the Wind Dukes of Aaqa make their final stand here three ages back? You've got that lovely campaign history, you might as well use it. Alternatively, you can use this ruin to unveil a heretofore unknown chapter in the history of your milieu. Sure, you could just chalk the whole ruin up to a local war of no import or a forest fire or something, but why not take the opportunity to make it a little more epic?
III - Snuff Out That Point of Light
So how wrecked does your location become? And it what ways? Redraw the map with some intact areas, some reduced to rubble and some structures completely scrubbed from the face of the earth. Look over the key for the original version and look for little details that pop out. Like, say, the mention of a blue velvet couch in the parlor of a rich merchant. Maybe that couch is still there, but it is dusty or mildewy, tattered or stained. Make sure your ruins are peppered with these small tokens of past lives. Also, add lots of cobwebs.
IV - Leverage Your Wandering Monster Charts
If the people move out, what moves in? Your local wilderness encounter charts should be helpful here. Obviously you want some sort of main monster to eat the PCs faces off, but don't forget to add some ordinary snakes or bats or things like that. And maybe some hostile mold or fungus.
V - Think About What Remains
What memories of this place still echo in the mortal world? Does the noble family that once ruled here linger on as the poor relation to some more powerful dynasty? Do the locals tell the story of how the place was destroyed, or why? Do you need to go back and add a weeping ghost or wailing poltergeist to the key? If so, the original adventure provides you with a bunch of possible people to haunt the place, as well as some leads as to what might be anchoring their soul to the spot.
VI - No Building Inspectors Here
Finally, consider adding some environmental hazards. No maintenance has been done to this place in decades, perhaps centuries. Walls may be ready to crumble, floors or ceilings can collapse. If you like the disease rules in your system, maybe the local water supply has gone off or perhaps there are rusty nails unwary adventurers can get tetanus from.
Obviously, this is a bit of a slog to do for every little rubble pile in your game. But if you need an upper level to your dungeon or a place to serve as the X spot on a treasure map, it ought to do some good work.
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