In the middle of the XV century on the site of the former Seljuk fortress of the knights of St John built the castle of St. Peter of green granite. The double walls of the fortress. The towers are called belonging to the countries that were part of the Order of St. John: English, French, German and Italian. In addition, there is another tower - the estuary or Harbour tower, which today serves as the main entrance to the castle. Another gate - the so-called "North entrance with a moat, leading into the main area of Bodrum and served as the entrance to the castle from the shore.

In its heyday, the castle was inhabited, perhaps 50 knights from seven different European countries and three times as a large number of ordinary soldiers. Their main task was the defense of the castle and its environs.

In 1453, the castle remained the only Christian fortress in the territory of Anatolia. At this time it was reconstructed, strengthened and built 14 tanks for water storage during the siege. However, in 1522, the castle surrendered and was soon abandoned. In the XIX century the castle was converted into a prison, and the chapel in the castle was transformed into a mosque.

Since 1960, there is a Museum of underwater archaeology, where underwater findings: amphorae recovered from the bottom of the sea, coins and weapons. Open Allais exhibited ancient sarcophagi, including the sarcophagus with a skeleton Princess Ada, the sister of the legendary Mausolus.