The cathedral has a heliometer (solar observatory) dating to 1690, one of a number built in Italy in the 17th and 18th centuries. The device itself is quite simple: a tiny hole in one of the minor domes acts as pinhole camera, projecting an image of the sun onto the floor at solar noon (12:00 in winter, 13:00 in summer). There is a bronze line, la Meridiana, on the floor, running precisely north–south. The ends of the line mark the positions as at the summer and winter solstices; signs of the zodiac show the various other dates throughout the year. The purpose of the instrument was to standardise the measurement of time and the calendar. The convention in Sicily had been that the (24‑hour) day was measured from the moment of dawn, which of course meant that no two locations had the same time and, more importantly, did not have the same time as in St. Peter's Basilica in Rome. It was also important to know when the vernal equinox occurred, to provide the correct date for Easter. The Orto botanico di Palermo (Palermo Botanical Garden), founded in 1785, is the largest in Italy with a surface of . One site of interest is the Capuchin Catacombs, with many mummified corpses in varying degrees of preservation. Close to the city is the Monte Pellegrino, offering a panorama of the city, its surrounding mountains and the sea. Another good panoramic viewpoint is the promontory of Monte Gallo (), near Mondello Beach. Moreton Bay fig of >30 m girth and of 32m height can be found on the Piazza Marina. This Ficus macrophylla is most probably the thickest tree in Europe. On the boulevard Via Roma is the Palazzo delle Poste an official Italian government building created during the Mussolini era in the stripped classicism architectural style. It was designed by the rationalist and later fascist government architect, Angiolo Mazzoni. Perhaps its most famous feature is the five mural cycle in the Futurist style painted by the artist Benedetta Cappa titled "Sintesi delle Comunicazioni" (Synthesis of Communication). UNESCO World Heritage Sites UNESCO World Heritage Sites include the Palazzo Reale with the Cappella Palatina, the Chiesa di San Giovanni degli Eremiti, the Chiesa di Santa Maria dell’Ammiraglio, the Chiesa di San Cataldo, the Cattedrale di Palermo, the Palazzo della Zisa and the Ponte dell’Ammiraglio, adding to the list that makes Italy the country