Mythburrow

 is the cavernous lair of Gelidon, the Nightmare in Ivory, found in the eastern Flotket Alps.

Description
This part of Flotket Alps has peaks 3000 to 6000 feet high. It contains a handful of caves.

There is a rocky outcropping on one side of the mountain that has a gradual incline with alternating steeper portions and plateaued areas. Further up, the outcropping rises to meet the actual mountainside.

Entrance
A few hundred feet up from the base of the mountain is an unnatural frosty expanse of white-blue ice, looking like a "plague of ice vines erupting from the mountain." In the center of the viney web of ice is a massive cluster of ice growths that encircle a 25-foot wide oblong cavern in the mountainside. At the entrance are snow and ice as well as some dead trees and rocks.

The Cave
The cave is 60 feet tall and 100 feet deep. On the western side of the chamber are makeshift leather tents. On the opposite end of the chamber is a wide 25-foot tunnel that presses further into the mountain. Inside the tents are numerous bones, caches of frozen meat, basic tools, climbing equipment and very simple drawings of a lizard-like creature with wings, depicted in an elevated, god-like position, with little yeti figures with their arms up beneath it, bearing gifts.

The Tunnel
The tunnel begins with a 25-foot wide entrance followed by a spiraling path. The walls are covered in ice, and stalagmites of ice appear in different areas. After 40 feet, the tunnel starts to incline before it continues as a fully vertical ascent.

Gelidon’s Lair
The lair is, like the cavern entrance, oblong in shape. It is extremely cold and entirely frozen, having been carved by Gelidon from an ice wall, with many sharp icicles hanging from the ceiling. The center appears similar to a frozen-over lake.

Towards the back of the lair, there are stone steps which lead up to a platform, which is lit by glowing purple lights which pulse. The dragon's horde is mostly embedded within the icy walls of the lair.

Society
A group of yetis inhabit the cavern in an apparently symbiotic relationship with Gelidon, bringing her offerings of food left at the base of the shaft leading upward to her lair. They camp in the cavern just inside the entrance, while Gelidon's lair lies deeper inside the cavernous complex.

History
Mythburrow is well-known to the people of the Greying Wildlands as the lair of an ancient white dragon, and a few adventurers have entered to seek treasure there, though as of 835 PD, none had been successful.

Essek Thelyss teleports the Mighty Nein and Reani to the base of the mountain in which Mythburrow lies so that they can get Gelidon to breathe onto their mithral, creating the iceflex they need to reforge the Star Razor. Despite the snowstorms in the region, the party is able to see the outside of the lair.

The party climbs up the mountain to Mythburrow's entrance and stays in Leomund's Tiny Hut as Frumpkin scouts out the interior, revealing the yeti society in the cave. Meanwhile Jester and Reani turn themselves into birds and scout out the surrounding mountains, and notice several yetis there, as well as a number of smaller caves. The Mighty Nein fight some of the yetis, and send Frumpkin forward again, learning that the tunnel continues in a spiral-like shape. They take a long rest in the dome, during which Caduceus and Fjord commune with Melora.

The next day, they travel through the tunnels to the point where the cavern becomes entirely vertical. Reani summons an ice spider and attaches the mithral to it, which gets Gelidon's attention, but the rope with which the party hoped to pull back the mithral breaks, requiring a recovery mission. Reani flies Jester, Nott, and Beau up the cave into the lair, where they can see Gelidon towards the back. They are able to locate the mithral - now iceflex - and they additionally take the Dispelling Stone and Elven Chain from the treasure horde. Gelidon is alerted, but everyone retreats to the dome, and Caleb teleports them out of Mythburrow to the Vellum Steeple.