The Riven Tower

From the introduction: The Warlock of Netherspire was renowned for his ability to summon – and banish – almost any entity. His manse sat on a charming peak…until ripped asunder by a rival’s sorcery, just as he was midsummoning! Now the ruins barely cling to the edges of a steep canyon. Lately, dreadful moans have been heard, and people are disappearing nightly. Can his secrets be recovered? Would-be explorers are advised to bring plenty of rope.