Nuraghes are prehistoric structures characteristic of Sardinia, built between 1900 and 700 BCE according to Wikipedia. About 7000 are known but there would once have been more. They come in a variety of forms and their function is not clear; they might have had various purposes and perhaps different nuraghes were used for different things.
This example is called Losa and is a whole complex of buildings, including later strucures from the Phoenician, Roman and medieval era.
Photo credit: Eiena https://commons.wikimedia.org/wiki/File:Nuraghe_Losa.JPG
The video at this site shows what a fascinating monument it is.