Portugal is home to several notable prehistoric caves that showcase ancient human activity, particularly through rock art and archaeological findings. Here are some significant prehistoric caves in Portugal:

1. Cave of Altamira - Although primarily located in Spain, this cave's art is closely related to the prehistoric sites in the Iberian Peninsula, including Portugal. It features stunning polychrome rock paintings of bison.

2. Cave of Figueira Brava - Located near the town of Sesimbra, this cave contains important archaeological findings, including evidence of human habitation dating back to the Upper Paleolithic.

3. Cave of Gruta da Lapa do Lobo - Situated in the Serra da Estrela region, this cave is known for its archaeological layers that provide insights into the lives of prehistoric peoples.

4. Cave of Aroeira - Found in the Lisbon region, Aroeira Cave has yielded artifacts from the Mousterian period, indicating Neanderthal presence in the area.

5. Cave of Escoural - This cave in the Alentejo region contains impressive rock art as well as burial sites and tools from various prehistoric periods.

These caves not only serve as important archaeological sites but also as cultural heritage markers, reflecting the early human presence in the region. For more information, you might explore resources on Portuguese archaeology or specific studies on prehistoric art in the Iberian Peninsula.