Madrid has a lot of hotels and other acommodation options.
These are the hotels closest to the colloquium venue:
Hotel Puerta de Toledo (3 stars)
Glorieta Puerta de Toledo 4
28005 Madrid
Tel: +34 914 747 100
Web: https://www.hotelpuertadetoledo.com/
Hotel Porcel Ganivet (3 stars)
Calle Toledo 111-113
28005 Madrid
Tel: +34 913 653 600