Dueling Chasm of Golthonor
The Dueling Chasm of Golthonor was a huge chasm in Dominarian Corondor that was formed from the explosion of power that was released after Dakkon Blackblade used the Black Blade to slay the Elder Dragon Piru after Geyadrone Dihada summoned her and Chromium Rhuell to fight him for her (though it was really all a ruse to get Dakkon to kill one of the dragons so that she could absorb the power from a dragon's soul). It was located in the Rift of Golthonor just east of the Spine.
Later, in the year 1281 by the Reckoning of the Sages of Minorad, it was where Jared Carthalion, Kristina of the Woods, Altair of Coloni, and Caliphear the Nightmare had a battle against Ravidel. Jared destroyed the various monoliths in the canyon with a powerful spell during the battle. From here, Ravidel launched his Mox Beacon, spreading his evil and then disappeared in the chaos of the crumbling monoliths of the chasm; Jared ascended and became a planeswalker in time to planeswalk away from the crumbling monoliths and save Kristina from falling or being crushed, though Altair was apparently killed.