I have a mod that makes Dragon Priests harder... So yeah, them. Volsung specifically, though. The mod makes him weaker... but he casts illusion spells that make copies of himself and disorientate you so you can't tell where the real one is.
Cyrodiil exploration is a lot more linear, though. When you're in Cyrodiil, if you're like level 5, you get a "boost" so you can even contend with someone who's say, level 20. That makes sieges a lot more fun when you can actually feel like you're contributing at a low level. I imagine the exploration is the same.