Opacity
https://opacity.us/
Urban exploration photography by Tom Kirsch. I have visited Opacity since I was a teenager in the early millennium. There is something about these photos of abandoned sites that just haunts me… And apparently many others.
Flavor: macabre
The Fantastic in Art and Fiction
http://fantastic.library.cornell.edu/index.php
An archived site by the Cornell Institute of Digital Collections featuring historical art of the grotesque, the bizarre, and the obscene. A truly fascinating site to browse while mulling over a hot cider and contemplating your next horror project.