Gatshadow Mountain

Gatshadow Mountain is an enormous, ominous mountain in Tal'Dorei at the southeastern tip of the Cliffkeep Mountains, just northwest of the Bramblewood Forest and Westruun. Gatshadow's peak is nearly always obscured by storm clouds or mist. The actual stone that comprises this monstrous formation is of a darker, more dense stone that is considered to be the finest for crafting on Tal'Dorei's continent, hence why many crafters and smiths make the dangerous journey there to quarry the rock—and not all return.

Pre-Stream
Vox Machina journeyed to Gatshadow early in their adventures, delving into the mountain itself:

"''Weeks pass, and Grog the barbarian hasn't been seen since suddenly leaving for the city of Westruun.  Heading there in search of him, the party meets his childhood friend—and their new companion—, the gnome cleric Pike.  Grog apparently hasn't been acting normally and had marched off on his own through the Bramblewood towards the ominous mountain, Gatshadow.  The party followed, dispensing with a troop of roadside thieves along the way, and wound their way toward the mountain.  Deep within, they encountered an abandoned subterranean city and eventually a crypt housing a mind-controlled Grog, the reanimated corpse of his father, Strongjaw, and a dying mage attempting a ritual to lichdom. Our heroes slayed the mage, but not before he could complete the ritual and embed his phylactery into Grog's chest.''"


 * –excerpt from

Umbrasyl's Lair
After the Chroma Conclave attacked in Chapter 4, the ancient black dragon Umbrasyl roosted in a cave at Gatshadow's peak, receiving tribute from Westruun. Several scouting parties from the Herd of Storms were sent to Gatshadow in preparation for an attack on Umbrasyl, but they didn't return. Later, Shale and some other warriors from the herd scaled Gatshadow, as well. Shale's age and disabilities slowed her down, so she survived Umbrasyl's slaughter of her party by a twist of fate, then descended from the mountain in time to meet Vox Machina. Together, Vox Machina and Shale ascended Gatshadow and slew Umbrasyl in his cave.