Ferry Bookings to Ustica. Buy your ticket on-line to the ports of the island of Ustica. Ustica a Sicilian island that is part of the province of Palermo. The island lies in the Tyrrhenian Sea and is characterized by the presence of numerous caves that stand out along the high rocky coast of Ustica. Among the most famous to remember are the Green Cavern, the Blue Grotto, the Golden Cave and the Cave of the Pillars. Shipping companies engaged in the ferry service connecting the island of Ustica are: Ustica Lines and Siremar.