Dolmen of Menga in Antequera, Spain. This is one of the largest megalithic structures in Europe and is dated to aprox. 3600 BC.

Menhirs in Atapuerca, Spain

Almendre's cromlech in Évora, Portugal

Arcaínha dolmen in Seixo da Beira, Portugal

Dolman of Axeitos, Spain

 

Stonehenge in the UK