Valley of the End

is just on the border of the Land of Fire and the Land of Sound. The story behind the Valley was that the two founders of Konoha, the First Hokage and Madara Uchiha had a battle there when Madara defected from the village. The battle was so great, that the two tore the earth itself apart and created the valley. The First managed to defeat Madara, and in memory of their duel, two statues were built on the side of the waterfall.

Sasuke Uchiha vs. Naruto Uzumaki
Many years later, a descendant of Madara, and the son of Fourth Hokage fought, Sasuke Uchiha and Naruto Uzumaki respectively. As with the fight between the First and Madara, Sasuke, aided by Orochimaru's Sound Four, made his way to the Valley of the End with Naruto in pursuit. As the two fought, both awakened great yet dangerous powers; Naruto slipped into his one-tailed transformation, and Sasuke activated the second level of his Cursed Seal of Heaven. In the end, the two attacked each other with enhanced versions of their signature techniques, a Nine-Tailed Demon Fox-powered Rasengan, and the Flapping Chidori, and in the end, Sasuke emerged victorious and continued to Orochimaru.

The Return of Madara Uchiha
Three years later, after the death of Deidara, Madara Uchiha returned to the valley and sat upon the head of his statue. While there, he mused on the growth of Sasuke's power, and his destiny.