Free entry to many of Fuerte's museums.
http://www.spain.info/en_GB/reportajes/espana_en_el_dia_internacional_de_los_museos.html
(http://i.imgur.com/v4Okt1k.png)
http://icom.museum/press-releases/press-release/article/launch-of-international-museum-day-2017-1/