We have some special discounts to stay at:
Single room: 57,42 €. Double room: 97,01 €.
Breakfast (buffet): 7,20€. Dinner: 14,30 €.
Single room: 50 €. Double room (single use): 60€. Double room: 70 €.
You can book it through the hotel website until August 8, 2016, adding the promotional code: "fallwordshop" (please notice the spelling).
From Sunday to Thursday: Single room: 45€. Double room: 54€.
Friday and Saturday: Single room: 65€. Double room: 74€.
You can book it through the hotel website indicating that you are a participant of the XXV International Fall Workshop on Geometry and Physics.
These are a few suggestions. The variety of hotels in Madrid is pretty wide, so feel free to book the most convenient for you.