Portoferraio is dominated by this massive coastal fortification built in 1548 by Giovanni Camerini. It's in a shape of a star.
Wikipedia (Italian) http://it.wikipedia.org/wiki/Forte_Stella_(Portoferraio)
Info Elba http://www.infoelba.it/isola-d-elba/territorio-storia/luoghi-da-visitare/forti-fortezze/forte-stella/
Address 22 Via Zambelli, Portoferraio 57037, Italy
Coordinates 42°48'56.999" N 10°20'0.6" E