The cave mesones on Cava de San Miguel

Cava de San Miguel runs along the west wall of Plaza Mayor and its mesones are built into the old cellars: Mesón de la Tortilla, open since 1960, Mesón del Champiñón with the mushrooms and a keyboard player, Mesón del Boquerón. Cheap plates, brick vaults, guitar some nights.
When: All year, evenings; fullest Friday and Saturday after 21:00.
Seen on DeTapasConRufo on YouTube, 24k views.
Photo Jorge Franganillo, CC BY 2.0, Wikimedia Commons.