The secrets of Gaudí and the Sagrada Familia, a terrific tour of small trains hidden under the main station, a mysterious hand, a fascinating amphitheater of dissection, an unsuspected air-raid shelter, a kiss of death, a museum tucked away in the back of a shop, a magic talisman on a street sign, secret Mason symbols, the emblem of FC Barcelona in Santa María del Mar? During the day and night, Barcelona reveals its secrets only to locals and travelers seeking to get off the beaten path. To that end, it is key to know where to go. An essential guide for those who think they know Barcelona well or for those looking to discover the hidden side of the city.