Sardinia is dotted with remnants of "nuraghi" (stone dwellings centered on a main tower or fortress) and "tombs of the giants" (monolithic burial chambers). These are what remind us of the so-called "Nuraghi Culture", the bronze-age people from the second millennium b.c. on the island. The sites are significant enough to be included on the UNESCO World Heritage List, represented by the Su Nuraxi nuraghi at Barumini (first photo,  below).

This is the nuraghi at Barumini. It is the largest one on Sardinia and is located in the southern part of the island roughly between Oristano and Caglieri.

The UNESCO description calls it "the finest and most complete example of this remarkable form of prehistoric architecture."

Also quite impressive is the Santu Antinenuraghi at Torralba, south of Sassari in the north. It is said to be the second largest structure of its kind. It is currently undergoing extensive work of restoration and preservation.

The large Albucciu nuraghi near Arzachena in the northeast (below and right)

The Buddusò nuraghi near the town of
that name in north-central Sardinia.

Li Loghi  (in the north near Arzachena)

Su monte è s'alpe just south of Olbia

Especially interesting are the tombs known
as domus de janas (house of spirits). They
were built by hollowing out large rocks to
form a funeral chamber within, leaving the
natural rock surface to serve as the outer wall.
This one is on the site of the S'Ortale e
Su Monte/San Salvatore complex near
Tortolì on the southeastern coast of the island.

There is other relevant, explanatory material on this website in the article about the monolithic monuments of southern Italy and in the general article about Sardinia. There is also information in the entry on Malta about similar structures there.