The Monolith from Beyond Space and Time

From the back of the book: "In the center of a valley that should not be stands a thing that cannot be. Those that go before the Monolith do not return the same as they left. Sometimes they do not return at all. An adventure for characters of any level, from zero to infinity, for use with Lamentations of the Flame Princess Weird Fantasy Role-Playing and other traditional role-playing games."