On the top hill, several miles from the city center, with a breathtaking view on Palermo from the various curves of the road going up the hill (mind: NOT from the destination itself), there is a place that seems to be very popular among the locals and tourists alike: the sanctuary of Sta Rosalia. Take the bus 812 from Teatro Politana and go until the last stop which is this chapel, cut in the rock of the hill Mte Pellegrino, and boasting the tomb of the Saint. I went there on Sunday, so I do not know if that was the reason, or maybe it is common so every day, though. Anyway, when there you find yourself among dozens of pilgrims (interestingly, many of them clearly of a Hindu origin) and even more... campers who massively come by cars (surprise: some of them even cleaned for Sunday purposes!) to the nearby forests to sit around, drink, eat and leave behind tonnes of garbage.
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