Riding the 'Train of Death' is dangerous. Michelle Frankfurter

The migrant caravan that trekked through the Northern Triangle and reached Mexico this weekend has swelled to an estimated 7,000 people, and is largely heading to the United States.

Most Central American immigrants that try to enter the US undocumented travel along the same dangerous route, known as El Tren de la Muerte ("The Train of Death").

Photographer Michelle Frankfurter spent years documenting immigrants traveling along the route.

Earlier this month, a caravan of 160 migrants set out from Honduras, telling media outlets that they were fleeing their homes due to widespread poverty and violence. By this past weekend, the caravan had swelled to an estimated 7,000 people.

Most are heading for the United States' southern border.

They aren't the first Central American migrants to chart that path. Approximately 400,000 migrants made the journey in 2016, with most hailing from Honduras, El Salvador, or Guatemala. Most looking to enter the US undocumented follow the same route north.

In 2009, Michelle Frankfurter , a photojournalist and human rights worker who had spent years traveling in Mexico and Central America, set out to follow the route.

Following the path described in Sonia Nazario's award-winning book "Enrique's Journey," Frankfurter headed to southern Mexico and followed the path north.

In six journeys, she rode the treacherous El Tren de la Muerte ("The Train of Death"), came into contact with drug cartels, and befriended numerous migrant families, many of whom never made it to the US.

Frankfurter has shared some of her photos with us here, but you can check out the rest at her website or in her book "Destino," available now .

Here's what the treacherous route is like: