This small tower is part of Fira de Barcelona (Barcelona Fair) venue. Easily spotted at the foot of the elevators leading to MNAC (National Art Museum of Catalonia) in the Palau Nacional, these beautiful towers are on almost every corner of the palaces on each side of the staircase. If you climb up till the museum you will appreciate the little turrets better and enjoy a panoramic view of Barcelona.
The Fira of Barcelona compound exists thanks to the celebration of 1929 International Exposition (World's Fair) at the slope of Montjuic hill. From that time are: Palau Nacional, the famous Font Màgica fountains full of colors and firecrackers during La Mercé celebrations (September 24th), Mies Van der Rohe Pavilion (rebuilt), the Olympic Stadium (remodeled) or Poble Espanyol. Here is another picture of a different tower.