Barbar is a complex of three 2nd and 3rd millennium BC temples, probably dedicated to Enki, the God of Wisdom and the Sweet Waters Under the Sea. The excavated complex can be seen from a series of walkways, which provide a great overview, though it's easier to understand with a detailed map.
Royal TombsThe Royal Tombs are the largest and most impressive of Bahrain's 85,000 burial mounds. Located in the village of A'ali the tombs may or may not have been the final resting places of kings, but they're definitely large: up to 15m (50ft) high and 45m (150ft) in diameter.
Qal'at al-BahrainAlso known as the Portuguese Fort, Qal'at Al-Bahrain is the country's main archaeological site. Beginning in the 1950s, excavations revealed the fort to be sitting on a tell, a hill formed from the rubble of previous cities. In all, seven layers of occupation were discovered, the earliest dating from 2800 BC.