Mythburrow

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

Description
The eastern Flotket Alps have peaks 3,000 to 6,000 feet high and contain a handful of caves. On the side of the mountain where Mythburrow is located, there is a rocky outcrop that has a gradual incline alternating steeper portions and plateaued areas until it eventually rises to meet the actual mountainside further up.

Entrance
A few hundred feet from the mountain base is an unnatural frosted landscape of white-blue ice described as "a plague of ice vines erupting from the mountain". At the center of that spiraling web of ice is a massive collection of ice growths that encircle a 25-foot wide oblong cavern entering the mountainside. The entrance is surrounded by snow, ice, rocks, and dead trees.

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 are stone steps which lead up to a platform lit by pulsing glowing purple lights. 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 teleported the Mighty Nein and Reani to the base of the mountain in which Mythburrow lies so that they could have Gelidon breathe on their mithral, creating the iceflex they needed to reforge Dwueth'var, the Star Razor. Despite the snowstorms in the region, the party was able to see the outside of the lair.

The party climbed up the mountain to Mythburrow's entrance and stayed in Leomund's Tiny Hut as Frumpkin scouted out the interior, revealing the yeti society in the cave. Meanwhile Jester and Reani turned themselves into birds and scouted out the surrounding mountains, noticing several yetis and a number of smaller caves there. The Mighty Nein fought some of the yetis and sent Frumpkin forward again, learning that the tunnel continued in a spiral-like shape. They took a long rest in the dome, during which Caduceus and Fjord communed with Melora.

The next day, they traveled through the tunnels to the point where the cavern becomes entirely vertical. Reani summoned an ice spider and attached the mithral to it, which got Gelidon's attention, but the rope with which the party hoped to pull back the mithral broke requiring a recovery mission. Reani flew Jester, Nott, and Beau up the cave into the lair, where they saw Gelidon towards the back. They located and recovered the mithral - now iceflex - and they additionally took a Dispelling Stone and Elven Chain from the treasure horde. Gelidon was alerted and chased them back to Caleb's Tiny Hut. As the dragon paced outside the dome, unable to penetrate with either claw or bite, Caleb teleported the party out of Mythburrow to the Vellum Steeple.