Ninendava. It's an Ayelid ruin just SE of HM's shrine (NE of Sancre Tor), and AFAIK the only quest involvement for that ruin is inside (an Ayelid Statue). I don't know what the roads look like for the route though... (I'm just looking at a map).
Edit:
Here's a road map I found somewhere (in case that might help):
Ninendava. It's an Ayelid ruin just SE of HM's shrine (NE of Sancre Tor), and AFAIK the only quest involvement for that ruin is inside (an Ayelid Statue). I don't know what the roads look like for the route though... (I'm just looking at a map).
Edit:
Here's a road map I found somewhere (in case that might help):