The Infinite — Douglas Clegg

Harrow is haunted, they say. The mansion is a place of tragedy and nightmares, evil and insanity. First it was a madman's fortress; then it became a school. Now it lies empty. But an obsessed woman and a ghost hunter want to bring the house back to life to find out what lurks within Harrow. Together they assemble the people who they believe can pierce the mansion's shadows.

A group of strangers, with varying motives and abilities, gathers at the house called Harrow in the Hudson Valley to reach another world that exists within the house....A world of wonders...A world of desires...A world of nightmares.