The Iron Necropolis

You know, as far as these things go the Iron Necropolis of Sapphire Sands is actually not that dangerous, especially when compared to the journey required to get there.

— Jasper Cameron, Leader of The Bronze Ravens

In the years following the Necromancer Wars the Iron Necropolis served as a sort of college for those who wished to learn more of the undead in a somewhat safe environment. Originally run by the Täysi Nolla, to this day it is still seen as a place where one can hone ones skills before heading out to the wider world... as long as you know the "back" way in.
To come upon the main entrance, grand as it may be, would require one to cross not just the Myrdhor Desert, but the Sapphire Sands as well. A journey of several months across the most inhospitable terrain with this plane has to offer, carrying all the water you need for the trip. Along the way one is likely to be hunted by jackalopes and worse.
Any who can make such a journey would be likely disappointed as they cut through the undead inside the necropolis, only to find a village inhabited by lore keepers (living ones at that) and their families nestled into a cleft at the base of imposing cliffs at the foot of the Outh Mountains.
This village has treasures of its own, for those that know of its reputation, for it is here that copies of The Book of the Unquiet Dead are made to be distributed out into the world. Printed on paper made from mushrooms that grow in and around the village, the book is an invaluable resource to those following the path of the Täysi Nolla or any number of other cleric and paladin orders.
Actually, speaking of mushrooms, the village is only able to exist because of the diverse mushroom species that grown in and around it. They provide everything from food and paper making materials to a wood like structural material and, yes, even the occasional recreational use. There are other strange idiosyncrasies to the village, but I will not discuss them here. Mostly so we can focus on the Necropolis.
A rather grand walled city, covering nearly a square mile on the surface, the Iron Necropolis is, as one may expect, full of undead. Usually nothing on the surface is more dangerous than Wight or banshee, as long as one stays away from Gallows Row or the execution square. Rumors say that this is due to an accord reached by the founders of the Täysi Nolla with the ruling lich of the necropolis. Rumors these remain. Honestly, most higher undead know better than to venture out into the sun, where their unholy powers are weakened
Also there are the runes, and the wall. Don't cross to other planes near the Iron Necropolis. The Ghostwalker Dwarves have not made an attempt in millennia to purge the place, but steps have been taken to ensure what is inside stays inside. That slight shiver you feel crossing into the shadows of the wall, sure part of that is the aura of the place, but mostly that is a sign that you have crossed the threshold of The Wall of Crimson Lace. As the more intelligent undead may be willing to tell you, there are fates worse than oblivion.