From the back of the book:
"The Great Mage Cheiromar, known as Aglahund the Mighty, is said to be buried under the Leaning Stone atop Galzar's Crag. One of his apprentices, Ulthorn, has been discovered dead in an aperture of the Leaning Stone...a doorway that locals swear has never been there before!
You must discover how Ulthorn died and the mystery of the Leaning Stone. In the process, you may find yourself at the Endless Stair. Those who never climbed it say it seems to lead to nowhere. Those who did never lived to tell of it.
Will you dare ascend into the unknown?"