This story helped propel 19th Century gothic fiction in the direction of "cosmic" horror. In fact, H.P. Lovecraft lists it as among his greatest influences. It begins simply enough: with two friends stumbling upon a ruined and curious house while vacationing in a remote village. After reading the tattered journal of the old recluse who lived there, they are shocked to discover an interdimensional, reality-bending nightmare full of nearly-indescribable horrors that range from demons, to bestial monsters, and devastating parasitic fungal diseases.
