The Mercado de Escravos (or Slave Market Museum) is situated in the center of Lagos on the site of a fifteenth-century slave market, believed to have been the first in Europe. The museum building itself was built in the seventeenth century on the remains of the market, first as the Royal Overseer's Office, and then as the Customs House from 1755. The museum seeks to highlight the history of Portuguese involvement in the enslavement of African people.

The opening displays in the museum provide the visitor with detail about the process of enslaved Africans being transported from Africa to Portugal, and how they were then integrated into Portuguese society. There is also a panel which provides information linking this to the slave trade in Brazil, which was then a Portuguese colony.

On the second floor of the museum, there are further displays about the slave trade. The collections include books, artefacts, archival material and pieces of art (both contemporary and historic). There are tablets available so that visitors can view more of the museum's collections that are not out on display.

The Slave Market also provides visitors with information about archaeological excavations on the medieval rubbish tip of Lagos, which have led to the discovery of skeletons thought to belong to enslaved Africans.