I love the thin rails (Anor Londo rafters). It's such a skill check.
I'd mastered running across those rafters to the point where in my own game I don't have to fight the painting guardians, I just run. It's my favorite place to invade, since I dive over to the flying buttress, run up there and across to the far side of the rafters where I can snipe them with Dragonslayer Greatbow as they slowly try to chase me. It's griefing-tier fun.