"Long ago, a small but mighty humanoid kingdom existed in what is now the local wilderness. Bugbear and ogre warriors fought brutal wars of expansion, earning great fame and amassing considerable fortunes from their predations. Those who died in battle were buried in large tomb complexes dug into hillsides and honored as patrons of the living. Among these tombs was the large tor known as Hightower. Though it was neither the largest nor the most famous of the kingdom's tombs, Hightower did represent a typical example of this kind of structure.
As happens to all such nations, the cruel humanoid kingdom eventually fell to a more powerful foe that razed all its cities and outlying fortifications. Of the tombs, only Hightower escaped destruction -- largely because it was an unimportant monument in a remote location. A few tribes of humanoids that survived the devastation tried to use it as a fortress, but the humans with whom they clashed defeated them soundly and sealed the entrance with a huge, round stone to ensure that the tor could no longer be used as a base. Since then, Hightower has served as a landmark for travelers in the know, but it has otherwise been largely forgotten.
But the electrical storms that have plagued the area in recent days have been quite severe, and a few weeks ago, a stray lightning bolt broke open the stone seal. Tonight, yet another terrible storm is sweeping through the wilderness, driving all creatures to take shelter where they can find it. Hightower looms on the horizon, and its door is no longer blocked. Will the PCs dare to enter its silent halls?"
From the WotC Website.