This is the main entrance to the central library. It's in the middle of a garden, so the whole building can't be seen, but it is shaped as a cross, with the dome over the crossing. It was founded in the 15th century as a hospital for the treatment of mental illness - apparently, the first of its kind in Europe. It has an "official" name nobody uses or knows; everyone in the city refers to it as "the library of the hospital".
Thanks for the photo. š