Ever since Hemmingway used the nine-day festival as the backdrop of his 1926 novel 'The Sun Also Rises', international visitors have flocked to take part in Pamplona's festival of San Fermín, or the 'running of the bulls'.
Half-tonne fighting animals thunder through the cobbled streets each morning while hundreds of runners, most wearing traditional white clothing and red neckerchiefs, scramble to avoid getting caught on their horns.
"It was thrilling, unforgettable, amazing – I don't think I have ever felt so exhilarated in my life," 26-year-old American law student Dale Carpenter told news agency AFP this year.
In a rapid-fire charge through Pamplona's narrow streets, the bulls arrive at the city's bullring.
Then, later in the afternoon, they are killed by matadors before their meat is served up in some of Pamplona's best restaurants.
But the hugely popular festival is fiercely criticized by animal rights advocates.
“Every shared tapa, every cerveza, every booked hotel room and balcony bolsters the killing,” wrote British poet Benjamin Zephania in the UK's Guardian newspaper.