On the right side of the church stands a 36 metre-tall bell tower. It contains a spiral staircase that gets narrower as you go up, making it difficult to get to the bells. However, the view from the upper part makes up for the difficulty.
The bell tower holds four bells. The Campana de San Bartolomé is the one which tolls on the hour. This bell measures 105 cm in diameter, 80 cm in height, and weighs 680 kg.
Along with the bells, the upper part also houses the mechanism used to wind up the clock since 1892. Around 8 years ago, it stopped working. Now, the bell tower clock works via satellite, using a photoelectric sensor that transmits the signal.