The main islets are "Illa Grossa", "La Ferrera", "La Foradada" and "El Carallot". The total emerged area of all four is around and the highest point is above sea level. Illa Grossa, by far the largest, is the northernmost island of the group. It stands in the place of an ancient crater and shows a distinctive semi-circular pattern. There are no buildings on it, except for a 19th-century lighthouse, a jetty and the staff quarters used by the biologists working in the wildlife reserve.