"The Willows" is without doubt the best and most frightening non-lovecraftian story of cosmic horror. To be honest, Algernon Blackwood is the only "non-lovecraftian", "non-mythos" but yet "cosmicist" author I know of to this day. Of course, Robert W. Chambers and Arthur Machen predate Lovecraft and the so called "Cthulhu mythos", but these authors and their works have become somehow incorporated into the "Mythos" themselves. Not so Blackwood. Albeit he is even cited at the beginning of "The Call of Cthulhu", his works have a distinguished unique motif and atmosphere.