My favorite mountain trek would have to be the Indian Creek trail in Arkansas.
As you come to a dead end in the valley, you have to scale a rock wall, and then make a 75 degree climb for 100 feet. This climb takes you to a cave. As you venture through the cave, you end up making your way through a tunnel within the rocks. This is called, "the eye of the needle".
Once you make it out of "the eye of the needle", you end up in a totally different valley. This valley is what remains of a dried up riverbed. As you follow the riverbed, you eventually come to a glorious 100 foot waterfall, that pools up at the bottom.