Founded in 1611 by Margaret of Austria, this convent near the Alcazar (to which it was linked by a passageway), benefited from the generosity of its royal patrons. Hence its fine collection of art works, in particular by the 17C Madrid School and, above all, an impressive collection of relics: there are over 1 500, including St Pantaleon's blood, contained in a phial, which is said to liquefy every 27 July.