A team of passionate anti-trafficking campaigners has just returned from an 11-day cycle that took in some of Europe's human trafficking routes.

The Freedom Challenge cycle started on October 6 in Sofia, Bulgaria and took in 10 countries, finishing on Wednesday afternoon in Westminster.

The purpose of the cycle was to raise money and awareness for the A21 campaign against human trafficking ahead of anti-slavery day today.

The cyclists hope to raise 210,000 euros for A21 shelters and victim assistance programmes.

Human trafficking is one of the largest and fastest-growing crimes in the world today, generating over $32 billion per year.

There are an estimated 27 million people in slavery today - believed to be more than at any time in history. According to A21, someone is forced into physical or sexual labour every 30 seconds.

Completing the challenge on Wednesday, cyclist Annabel Partridge recalled some of the shocking scenes she witnessed along the way, like cycling past brothels in the Netherlands and Belgium where girls were dancing in the windows.

Women and children are often kidnapped into the sex slave industry, with 12-years-old being the average age of a trafficking victim.

Partridge explained: "Going from Bulgaria and Serbia, which are very much the source countries, you just see the poverty in the area and you understand why the girls will move out.

"We stopped at a truck stop one day and one of the guys who drives the van got offered if he wanted a girl in a little cafe. There's an 80 to 90 percent of women are trafficked, only 10 per cent actually choose to be there. So it's hard when you know that."

Hillsong Australia Pastor Ben Houston decided to take part in the Freedom Challenge despite suffering from pain in his scar tissue and arthritic joints - the result of being a child athlete.

During the cycle, the team rode 48 kilometres up Alpine Road, which leads to the highest mountain in Europe, Grossglockner in Austria, with its 36 bends and an altitude ascent to 2,504 metres.

Houston explained how physically challenging this was, saying it "took a lot of strength to go through".

Professional cyclist Dean Windsor led the team on the 270-hour cycle. Speaking yesterday, he admitted that doing so was his "biggest challenge" personally, as only a few had a lot of cycling experience.

He said: "To keep the team safe and to get them to have the skills and fitness to finish the ride was probably the biggest challenge for me.

"Even though I tried to train them as much as possible, the challenge actually took a lot more heart than fitness in the end."

The team of cyclists also included 37-year-old Lindz West, lead singer of Christian hip hop group LZ7, and Hillsong London Pastor Dan Blythe.

Windsor said the team constantly reminded themselves of the purpose of the challenge to get through it.

He said: "It was mentally and physically beyond their limits but they pushed through it and I don't think they lost sight of the cause.

"The motivation wasn't about having a beautiful ride through Europe, the motivation was for A21 and to stop human trafficking. The morale was always high in our team because we were doing it for such a great cause."