I'm currently playing Alpha Protocol, a nice espionage RPG by Obsidian. It has ladders that you climb to reach higher platforms and to my big surprise, the NPCs know how to use them! I think Skyrim being such a big open world with big cities would benefit a lot from vertical development if they added ladders, ropes and NPCs that use them to climb. What do you say?

I say there hasn't been ladder climbing in any TES interation.

TESA: Redguard had climbing though, by far and sadly the most advanced vertical movement of any TES game ever.

I remember Todd Howard said something at some point about ladders being some of the things they didn't manage to make work. I would personally like ladders that you actually use instead of loading screen, could enhance the stealth gameplay in cities with alternative paths and all.

That's exactly where npc a.i. should be heading: the npc world awareness. They should know how and when to use the terrain and the geography in their favor. For instance if you crouch into a rat hole to escape your pursuers they should grab a torch, crouch and come after you. Same if you jump on a roof and shoot arrows from there they should bring a ladder and come after you. That's radiant a.i.

Daggerfall has a climbing skill?

Yeah, Daggerfall had climbing. You could scale the city walls and stuff to get in and out of town. Of course, it also had flying so climbing wasn't really needed.