Here's the website address:
http://www.hostal-alcazar.com/ I had a look at frommers.com, too:
'Conveniently located in the midst of Madrid's best shops is this post-World War II building, complete with a circular Greek-style temple as its crown. On the building's fifth floor, you'll find long and pleasant public rooms, wood panelling, lead glass windows, parquet floors, crystal chandeliers, and high-ceilinged guest rooms.'