This is not a place you ride to. Hayr Bu Thamah is an oyster bed out in the Gulf, northeast of Bahrain's Muharraq island, and on a map it is a dot of open water with nothing around it. For centuries the pearl divers of the Gulf set out in wooden boats to beds like this, dropped over the side with a nose clip and a basket, and came up with oysters that made the region rich long before oil did. Bahrain's pearling heritage, including the oyster beds, the old merchant houses in Muharraq and a coastal fort, is listed by UNESCO as a testimony to that island economy.
Pearling was brutal work. Divers worked from the boats for months in the summer season, held their breath for a minute or more, and often ended in debt to the captains who financed the voyage. The trade collapsed in the twentieth century when the Japanese began culturing pearls, and the finding of oil in the 1930s gave the Gulf another way forward. The old song traditions of the pearl boats, the sea songs called fijiri, are still performed in Bahrain today and are worth hearing if you get the chance.
What you can ride is the shore and the island next to it. Muharraq, linked by causeways to Manama, has narrow streets, a restored pearling trail of old houses and a souk, and the riding is slow and urban with some traffic. Roads on the main island are flat and fast, with wide highways, roundabouts and a lot of heat. Winter, from November to March, is the pleasant season. In summer it is hot and humid, and a ride in the evening is much better than at noon.
Fuel is plentiful and generally cheap on the island, and the causeway to Saudi Arabia, the King Fahd Causeway, is a famous piece of engineering, though border formalities apply and you should check your documents and insurance well before planning to cross. If you are on the water, you can arrange boat trips from Muharraq to look at the area, though the beds are protected. Try a plate of machboos, the spiced rice with fish or lamb, and a cup of cardamom coffee while you think about the divers.