Castel dell'Ovo (in Italian, Egg Castle) is a seaside castle located on the former island of Megaride, now a peninsula, on the Gulf of Naples in Italy. The castle's name comes from a legend about the Roman poet Virgil, who had a reputation in medieval times as a great sorcerer and predictor of the future. In the legend, Virgil put a magical egg into the foundations to support the fortifications. Had this egg been broken, the castle would have been destroyed and a series of disastrous events would have involved the city of Naples. The castle is located between the districts of San Ferdinando and Chiaia, opposite the zone of Mergellina.
In the 19th century a small fishing village called Borgo Marinaro, which is still extant, developed around the castle's eastern wall. It is now known for its marina and restaurants. The castle is rectangular in plan, approximately 200 by 45 metres at its widest, with a high bastion overlooking the causeway that connects it to the shore; the causeway is more than 100 metres long and a popular location for newlyweds to have their wedding photos taken. Inside the castle walls are several buildings that are often used for exhibitions and other special events. Behind the castle there is a long promontory once probably used as a docking area. A large round tower stands outside the castle walls to the southeast.