Aside from the drawcard of beautiful beaches Kos has an abundance of interesting ruins to explore and is easily reached from Rhodes or Bodrum by ferry. Kos was prominent in antiquity because of its healing temple of Asclepius, founded after the death of the famed physician Hippocrates, who allegedly taught students on the island. The island also features the remains of temples for other healing deities including Isis and Sarapis, and appears to have historically been an island healing retreat. The island boasts a tree that is reputedly the oldest in Europe and Hippocrates is said to have held lecture sessions in its shade. A Venetian style castle built by the Knights of St John in the 15th century, guards the harbour. The island also has several archaeological remains of Persian, Turkish, Roman and Byzantine conquerors that all added their bit during a long history. Kos has busy bars and an entertaining nightlife, and there are some pleasant towns and beaches outside the capital.