Coatepeque Lake is a volcanic lake situated about an hour from San Salvador. It is much older than Ilopango, though created by a similar catastrophic eruption some five to six thousand years ago. Named Lago de Coatepeque, it is on the eastern slope of the Santa Ana volcano. It is a beautiful, clean, and sparkling blue crater-shaped lake, 6 kms wide and 120 meters deep and surrounded by steep green slopes rising up 250 to 500 meters. The scenic road between the Interamerican Highway and CA8, known as the “panoramic highway” for its marvelous views, curls along the steep ridge of the crater giving you glimpses of the broad fertile valleys on one side and the lake on the other. http://
Seawater pool: before kids come to play, pee and poo, I am there, doing my circular nonstop 4km swim. Great daily workout 
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My EL SALVADOR hostel: Los Cobanos Village Lodge
[Photo credit: Wikimedia Commons.]