Best exploration oriented quest you have experienced?

[jaybirdy]

Arcanum: Cross that mountain

That's a pretty esoteric joke (I hope), I haven't seen much complaint about the mountain range. There should be though, as it was an awful idea all around. There were only three ways to cross it: you can either wait for the story to guide you to the path, wiki the coordinates, or hit all the suspicious spots on the map and go screen to screen in a rampant, autistic search.

Arcanum - Jewish/Half Ogre conspiracy

Now this was a great frickin Arcanum quest, possibly the single best quest in an RPG. Hints of the conspiracy popping up through the whole game, sailing to the island and finding evidence of the plot, the newspaper guys that gave you the details playing stupid and then disappearing, and just to make you feel powerless against such a conspiracy, they don't give you a way to complete the quest. Brilliant