House on the Borderland by William Hope Hodegson

One of the most influential supernatural horror stories ever written by British author William Hope Hodegson and first published in 1908.

The book concerns two gentlemen holidaying in rural Ireland who come across a manuscript which is a written account by a recluse of his experiences in an ancient now disappeared house 'long given over to evil and founded on grim arcane laws'. The house is built upon an abyss like chasm from which humanoid pig-like creatures which the recluse calls "the swine-things" emerge. The swine things embark on violent nightly attacks on the house and the recluse has to fortify the building to ward off the attack. As the novel progresses it becomes increasingly hallucinogenic and the House seems to be situated upon an inter-dimensional fault line which leads to the recluse experiencing bleak and melancholy visions which seem to span the whole of time and creation.

It's an incredible novel far ahead of its time and perhaps its highest accolade is that it was a great influence on H.P Lovecraft.