Usually because a book in-game has mentioned it and its description appeals to me. Or there's rumored to be some lost treasure that appeals to me.
"According to this dusty old thing in the library, a gem allowing one to transcend death is believed to have been taken to these ruins in Not-Mayan Snakeman country" definitely a winner,
I travel to new areas because I enjoy the uncertainty of what lies around the corner. You get that feeling like walking down a dark road at night and you hear a stick snap in the woods, that feeling that washes over you and tingles in anticipation, or your just scared like heck. Your not sure whether to start running or turn around and look at the spot you heard that noise. Or for the big city folks it's like walking down that back alley and seeing that dark figure standing at the end against a building and your left deciding whether to continue walking or go back and take the long way around. It's that feeling that drives the true adventurer. I look forward to the day I can experience that feeling in Pantheon
Resources only available in that area
Something about it that stands out like enhanced experience or cash
To check out an area that may be completely different from the rest of the world
In EQ1, I remember going into a zone or a new area, just to see what was there, pure and simple. "What's at the top of that hill?", "Is there anything deep in the woods?", "What's that light in the distance?", "Can I climb to the top of that mountain?", etc.
Most of the time, there was not much in those none-standard, difficult to reach areas, though (shame!). Sometimes I was rewarded with something unexpected or a great view. That really is enough for me; exploration and finding unexpected stuff and/or great views. Much like in RL.