We visited this site recently after seeing both Bahraini's WHSs. We drove towards the Oil Museum, then back through many burial mounds and ended up in the village Barbar. There are three temples on this site, one on top of another, the oldest one dating 3000 BC. The culture was Dilmun, the temple apparently dedicated to the diety of the freshwater. There's a well with steps leading down towards it as a part of the site. The most popular find was the head of a copper bull that's one of the symbols of Bahrain and a symbol of the site. It can be found in the National Museum in Manama. 

The site can be found off the main road, it's signposted. In front of it is a large sports playground, parking spaces are available. There's no entrance fee, you just wave to the guy guarding the place. There's a lovely paved footpath circumnavigating the diameter of the excavation site. As a part of the efforts towards subscription, a brand new visitors' centre was built. Info panels are in English and they tell the history of the site, archaeological digs and have interesting pictures. The overall visit takes no more than 30 minutes and is easy to do when you navigate around Bahrain with a rental car.