Glassed Cavern in Fallout 76 is a location players need to visit if they want the Ultracite Power Armor and to complete certain missions in the game. 

The glassed cavern is a location in the Cranberry Bog region of Appalachia in 2102.​

Glassed Cavern Fallout 76: How to Get There

Head to the AMS Corporate Headquarters in the Cranberry Bog region and head southeast. It is toward the edge of the map and you'll find the Glassed Cavern. 

For PS4 fans, Fallout 76 1.07 Update hit PS4, bringing a huge number of changes and fixes to the game on that console.

In terms of more interesting changes, the update targeted a few balance problems from Bethesda's perspective. It increased the bonus damage provided the Gatling Laser by the Charging Barrels mod. Bobby pins now weigh less, and, perhaps most importantly, Bethesda removed the exploit allowing players to farm Glowing Ones for an excessive experience.

Photo courtesy of Bethesda