Charco de los Sargos is one of El Hierro's black-rock bathing spots, cut into the volcanic coast of El Golfo. It is less polished than a resort beach: the appeal is the rough lava, clear Atlantic water, and the sense that the island has shaped the swimming pool itself.
Treat it with respect. Conditions can change quickly, and this is better for confident swimmers than for anyone expecting sand, lifeguards, and easy water. On a calm day it is a memorable stop between the better-known pools and viewpoints of the Frontera coast.