They hope to reach Italy and the wider EU.
But often migrants find themselves trapped in Libya, and victims of widespread and horrific sexual violence.
These are the findings of a study by the Women's Refugee Commission - shocking those who led it.
(SOUNDBITE)(English) SEXUAL VIOLENCE PROJECT DIRECTOR AND CONSULTANT FOR WOMEN'S REFUGEE COMMISSION, SARAH CHYNOWETH, SAYING: "I have worked in humanitarian aid for around 16 years and over 20 emergencies and these accounts were among the worst that I have ever heard.
They are quite disturbing." The study focused on crimes against men and boys.
Researchers said when they asked them about sexual violence they said things like "this is normal in Libya" and "this happens to everyone." The findings are deeply alarming.
Testimonies included people being forced to rape corpses, castration, and forced incest.
There were many cases of people being killed for refusing to participate, or being filmed to extort money from relatives.
(SOUNDBITE)(English) SEXUAL VIOLENCE PROJECT DIRECTOR AND CONSULTANT FOR WOMEN'S REFUGEE COMMISSION, SARAH CHYNOWETH, SAYING: "It is also used for punishment and control of detainees in both official detention centres as well as unofficial places of captivity.
We heard a number of times how if a man tries to escape the detention centre and is caught, he is brought back and all the other men in the detention centre have to rape this man." The study warns refugees and migrants are trapped in a nightmarish web of extortion, exploitation, abuse and sometimes slavery in Libya.
A place thousands are sent back to by the EU.