Dozens of demonstrators lay half-naked on the streets of Pamplona on the eve of the San Fermin festival on Thursday.
The activists, brought together by AnimalNaturalis, were protesting both the bull runs and bullfighting that occur daily throughout the event.
At the festival, hundreds of people run from bulls, bred especially for the event, through the narrow streets of Pamplona. While San Fermin hosts many kinds of traditional shows and activities, it is primarily known for the bull run, which ends daily at the Pamplona bull ring.
Following the run, the animals partake in a bullfight event consisting of three stages, according to animal rights organization PETA. Bulls are first attacked with lances by "picadors", then harpoons by "banderilleros" and finally a sword, among other weapons, by the "matador", it said.
The organisation estimated across the entire San Fermín festival, at least 48 bulls are "stabbed to death".
Supporters argue that bullfighting is a hallmark of Spain's cultural heritage.
While PETA reported that more than 125 towns have declared themselves anti-bullfighting, San Fermin attracts more than one million people to its festival every year.