The sturdy stone castillo was built in the 16th century to fortify the harbor after Drake’s raid and later served to hold prisoners and sailors who arrived in port with infectious diseases. It became a museum in 1968. Some artifacts date back to the mysterious megalithic culture of the late Paleolithic era, while others were discovered in medieval burial sites. There’s also Roman metalwork and pottery, but visitors are most amazed at the level of artistry in the Celtic gold jewelry created 2500 to 500 b.c.