The Caves of Poço Velho (old well) are located in the centre of Cascais in the Lisbon district of Portugal.

In 1880, they were visited by members of the IX session of the Congrés Internacional d'Anthropologie et d'Archéologie Préhistoriques (CIAAP) (International Congress of Anthropology and Prehistoric Archaeology), which was being held in Lisbon that year, although it seems that the participants might have been a bit worse for wear on the morning of their visit as they had arrived in Cascais the night before during birthday celebrations for the Prince Royal.

At the end of the 1800s another researcher, José Leite de Vascocellos, warned of the state of degradation of the site due to growing pressure from building construction.

However, subsequent work has found that the main occupation of the caves took place in the neolithic and chalcolithic periods (4th and 3rd millennia BC).

In 1942, Afonso do Paço carried out the second major exploration of the caves and between 1945 and 1947, the archaeologist, Abreu Nunes, carried out new excavations that discovered different funerary remains, including: polished and chipped stone artefacts; limestone votive offerings, such as cylindrical idols; decorated schist slabs, and ceramics.