HI im looking for some ruin (dark stone) walls. Pref broken down and ruin towers...think of The Lord of the Rings...The watch tower that Frodo got stabbed.....that kind of stuff.
You could try Flight from Covenant from the TFL campaign (rip them from The Fallen Levels?). Lots of ruined towers/walls. If you want them darker/different textures it might be a bit of a pain though (dup files, change tag ID to something unique, point GEOMs to new CORE, make new textures with Amber).