San Julián de los Prados, Oviedo.

San Juián, aka Santullano, was on of a little clump of pre-romanesque buildings that emerged in Asturias in the 9th and 10th centuries. There´s information about the church in Wikipedia - unfortunately it won´tlet me copy the page for you; 
and there´s information about Asturian pre-romanesque at   https://www.spain.info/en/top/asturias-pre-romanesque/
And for those who like pre-romanesque windows there are some on the east wall, shown in the extra.