From Callosa take the Parcent road , follow it for 21 ? a2 km ( 11 ? a2 miles ) , and make a right-hand turn at the entrance to the El Algar waterfalls , a tumbling oasis beneath the massive Sierra Bernia formed by a tributary of the River Guadalest .
It 's been said that the Sierra Bernia is the only structure of its type in the world .