Heather got into a taxi at Barcelona airport. Moments later, she had a spine-chilling realisation.

Heather Bailer never imagined she could be a victim of human trafficking.

But when she hopped into a inconspicuous taxi shortly after arriving in Barcelona, she fears that could have been her fate.

Heather, a college graduate from Atlanta, Georgia, believes she narrowly escaped becoming a victim of human or sex trafficking.

Writing on Facebook after returning from her trip to Europe, Heather has shared her terrifying story, which has now received over 25,000 shares.

When Heather landed at the Barcelona international terminal, she had trouble finding the taxi bay until she saw a group of men “speaking perfect English” offering taxis.

She approached the men and one of them led her to a line of unmarked cars which looked like taxis.

Heather, who had previously studied abroad in Barcelona and Madrid was well aware that Barcelona has both typical yellow and black taxis as well as normal unmarked cars (similar to Ubers).

Unfazed and seeing other tourists getting into the cars around her, Heather hopped into a car being driven by a man in his sixties.

But once she hopped in, Heather had a spine-chilling realisation.

As Heather got in the car, the man who led her to the 'taxis' immediately hopped into the passenger seat of the car as the driver locked the car doors.

"Obviously this was immediately scary to me because why do two men need to drive one person in a taxi?" Heather wrote on Facebook.

The men began to talk among themselves, ignoring Heather's requests to be dropped at her hotel, so she decided to check Google maps to see if they were heading towards her hotel.

"I instinctively did this and immediately realised they were taking me the opposite way of the hotel," Heather explained.

She had to come up with an escape plan. Fast.

"All this time I was speaking English since the guy was talking English to me, but I speak Spanish pretty proficiently and began to talk in Spanish to the guys," she wrote.

Watch: Mum's 'human trafficking' warning goes viral.

"Both of the guys snapped their heads around and were really taken aback that I could speak Spanish. They were definitely wondering how much of their conversation I had understood."

Heather began to question the men in Spanish, asking them why they were going in the wrong direction and telling the men that her friend was expecting her in 10 minutes.

At this point, Heather had been in the car for 25 minutes, for a trip that should have taken only 15.

"The first guy then turned around and started talking about how beautiful I was, asking how old I was, asking if I had a boyfriend, and asking how long people would be expecting me gone in Europe,

"It became very clear to me before this point, but EXTREMELY clear to me at this point that these guys could potentially be trying to kidnap me into something, presumably sex-trafficking."

Heather rose her voice, leaving the men flustered after telling them that she knew where they were taking her.

"They looked at each other and said, 'necesitamos cambiar los planes' which in Spanish directly translates to 'we need to change the plans'," she said.

"I said I know what you all are trying to do and people will come looking for me and the men look at each other, the older man driving accelerated across six lanes all the way from the left to the right, and turned the corner, and just said, "get out here" in Spanish. I grabbed my bags and quickly got out of the car and they drove away, obviously not asking for money or anything since clearly this wasn't a taxi."

"If I didn't speak Spanish I truly don't know what would have happened."

Heather added that she wanted to share her story to warn other that human trafficking can happen to anyone.

"It's an unfortunate reality that women need to keep their guards up while travelling or taking taxis/Uber alone," she wrote.

"But as much as we want to see the good in everyone, some people have bad intentions that we need to be aware of."