This is the Salt Valley of Añana Basque Country, northern Spain.
Lovely site. This site has been used to gather salt for a long time. The first documented use of it dates 882AD, but the site has been used way before that.
The salt comes from the Triassic period, when it was all underwater before the separation of the continents.
They have habilitated it with some salt water pools and a shop of the local produce.
Great place to visit