Santo Spirito al Castel di Guido is an old parish church at Piazza Castel di Guido 8, in the old rural village of Castel di Guido north of the Via Aurelia in the far west of the municipal area.
This church is in the municipality of Rome, but belongs to the diocese of Porto Santa Rufina.
It is a cylindrical building with a roof pitched in eight triangular sections, and has its origins in the 18th century. The attached façade, which has a pitched roof hipped at the sides, is rendered in grey with white marble architectural details. Two pairs of Doric pilasters are at the corners, and support an entablature with a very deep blank frieze. There is an internal loggia, entered through an archway with a pair of columns in the round having imposts but no capitals. There is no walling between these columns and the inner pilasters, and these two gaps are as high as string courses which are continuations of the arc of the archway.
There are ancient Roman remains in its crypt.