Perched on a steep hill north of the city, the extensive ruins of Mitilini's castle are fun to explore and offer fine views of city and sea from the ramparts. The kastro was founded by Justinian, in the 6th century A.D., and was restored and enlarged, in 1737, by the Genoese. The Turks also renovated and built additions to the castle during their occupation. In several places, you can see fragments of marble columns in the castle walls -- these are blocks from a 7th-century-B.C. Temple of Apollo, taken by the Genoese. Look for the underground cistern at the north end of the castle precinct: This echoing chamber is a beautiful place, with domed vaults reflected in the pool below. In summer, the castle is sometimes used as a performing-arts center.