A kitsch former knocking shop - ask for the room with the mirrors on the ceiling and the bath in the middle (room 20). This is where King Alfonso XIII used to meet his mistresses whenever he felt like cuckolding Queen Victoria's granddaughter, Victoria Eugenia (which was a lot, as at least three bastard children can confirm).
Calle Barbieri, 5; Tel: 91 522 4630; Metro: Gran Via
This hotel is sadly closed, or being refurbished for a long time.