El Valle de los Caidos- one of the creepiest places I have ever been to. A fascist monument comissioned by Franco and to this day remains to be one of the largest mass graves in Europe. During its erection it was used as a labor camp for Franco's opponents/prisoners, most of whom died there.
Today it is open to the public and functions as a lovely catholic church where one can attend Mass and also leave flowers for dead fascist dictators. Francisco Franco was buried here and to this day El valle is a place of peregrination for Franco supporters on the right (and there are many and growing!) Needless to say it is one of the most controvertial, discusting reminders of Spain's undealt with history, memory and trauma.
For more info on El Valle de los caidos:
www.bbc.co.uk/news/world-europe-14189534
If you like scary, haunted places that make the blood boil then visit my blog. There you can see a few photos of an ongoing personal photography project/obsession. It centers on an abandoned, 1950's hotel right next to the monument.
mariolarosario.tumblr.com/