Street photographer Alberto Verdu Martinez is captivated by the festival of San Fermin in Pamplona, Spain.

The spectacle surrounding the eight-and-a-half-day running of the bulls -- more than the daily, life-threatening action of the animals themselves -- has inspired him to return to the event over the last 15 years.

"For me, it's about the people who attend San Fermin, how they live the fiesta," Verdu Martinez , who is from the southeastern Spanish city of Monovar, told The Huffington Post this week. "I don't really concern myself with the running of the bulls or the bullfights."

The photographer has taken many stunning images of the festival over the years, including these from 2014 and 2015, which have never been published previously.

"I just walk aimlessly through the streets and try to transform regular situations into the extraordinary," Verdu Martinez said.

This year's festival begins Wednesday , with the first run taking place the following day at 8 a.m.