You have the opportunity to visit singular buildings in the city, ie. Palau Moxó, a palace built in 1770, on the bases of an ancient palace from the 13th Century. It was the most important private residency in Barcelona during the Middle Ages. It is also known as the Palace of the Marquis of San Mori, one of the most aristocratic family, married to Francisca Güell, a daughter of the Viscount Güell, Gaudi’s sponsor.
Visits to some of these buildings require to be pre-arranged and in some cases it also requires a minimum group. Please note these are NOT tourist attractions.
http://www.casessingulars.com/ -singular buildings website
http://www.palaumoxo.com/ -Moxó Palace
http://www.racba.org/en/ -Catalan Royal Academy of Fine Arts
http://www.racab.es/en/ -Barcelona Royal Academy of Sciences and Arts
http://www.ramc.cat/ -Royal Academy of Medicine of Catalonia
http://www.rocamora.es/ -in Spanish only.
The audio is in Catalan yet the video will give you an idea on what to expect when visiting the place.
Video: © Barcelona Cultura