Complex sentence: One of the rooms leading off the courtyard contains the Shipwreck Museum, which exhibits the remains of a Greek merachant ship from the 4th century BC, one of the oldest vessels ever to be recovered, together with its cargo.
Split into simpler sentences: One of the rooms leading off the courtyard contains the Shipwreck Museum. The museum exhibits the remains of a Greek ship from the 4th-century BC, which is one of the oldest vessels ever to be recovered, together with its cargo.