Yeah, there are several things that came in 1.8 but they're all distinct:
* Ravines, which cut through the landscape.
* NPC villages (currently lacking NPCs.)
* Abandoned mineshafts (where you find cave spiders.)
* Strongholds (underground castles with silverfish and whatnot.)
I believe some of them are usually found close to each other but they are not by any means the same thing.
Strongholds have iron doors and their walls are made of stone brick, so that's what easily sets them apart.