A woman from Kent and a man from Sussex are among up to 1,000 people expected to take part in a naked protest against an annual Spanish bull run.
The Running of the Bulls saw eight people injured in 2004
The town of Pamplona, in northern Spain, will witness the fourth nude "Human Race" on Tuesday before its own traditional Running of the Bulls.
Ivan Darch, of Hastings, and Alexandra Egre, of Canterbury, are from People for the Ethical Treatment of Animals.
They left the UK on Sunday to join up with the PETA campaign in Spain.
Supporters from across Europe will march through the streets of Pamplona to voice their objections to Thursday's bull run.
PETA said many of them will be naked apart from red scarves and plastic horns.
Sean Gifford, director of European campaigns, said: "Tormenting and butchering animals for entertainment is something straight out of the Dark Ages."
Ivan Darch said the naked march gets a mixed reaction in Pamplona
Bull runs and bullfights with matadors are described as a "vital" part of the San Fermin festival in Pamplona.
But Ivan Darch called it a "historically cruel and barbaric tradition that really needs to be put to bed".
Mr Darch also supported PETA's protest in 2004 because he thinks the Running of the Bulls is "morally wrong".
"It has been outlawed in certain towns in Spain, so I think it's a case of slowly but surely.
"As long as we keep up the fight at our end, then people will see we're not going to go away or stop until we get the results that we need."