The true weird tale has something more than secret murder, bloody bones, or a sheeted form clanking chains according to rule. A certain atmosphere of breathless and unexplainable dread of outer, unknown forces must be present; and there must be a hint, expressed with a seriousness and portentousness becoming its subject, of that most terrible conception of the human brain--a malign and particular suspension or defeat of those fixed laws of Nature which are our only safeguard against the assaults of chaos and the daemons of unplumbed space.
Or as I call it, Thursday. Interestingly, Lovecraft's feel for the tone of shifting perception was mentioned in this article on four-dimensional space and topology. The author, Richard Elwes, uses Lovecraft as an intro to his notion that four-dimensional spaces are remarkably similar to the shape of Yog-Sothoth as Lovecraft described it. Perhaps that's all we should say about that, lest eldritch horrors appear.
You're feeling courageous? What about an automatic sanity check fail? Here's a mashup of Stephen Colbert and Cthulhu, intended for 3D printing at Thingiverse. Never heard of 3D printing? It's just the most awesome thing ever. Almost as awesome as finding two Lovecraft references to start your day. Tip o' the hat to BoingBoing for both of these.