The town of Granadilla had to be abandoned to make way for the Gabriel y Galán reservoir. I thought that the town was submerged beneath the waters but it turns out that it remains on dry land and is slowly being rebuilt. You can actually visit the town, an excursion which I assure you is worthwhile. The old Granadilla city walls still stands and you can walk the walls and towers and take in the great views of the town and the surrounding reservoir. There are also plenty of companies that offer activities and watersports in the reservoir.