Here in the US, we tend to think something like a 200-year-old barn is "old." Then someone makes a discovery like the one a construction crew in Madrid, Spain, recently unearthed, putting that barn in perspective.
A construction crew working on a forthcoming flagship Apple Store at number 1, Puerta del Sol in Madrid have come across the remains of what appears to be a 15th century hospital. The site was formerly the location of a hospital that was demolished in 1854 to make way for a square. While the ruins will be covered back up, the floor will be outlined to mark their presence, and a plaque will explain the outline.
As of this time, it's not known if the marking or the plaque will be publicly visible or only accessible to employees, as they'll be on the store's basement level.