Beach of as Catedrais Nature · Ribadeo, Mariña Oriental, Lugo The beach of Augas Santas, declared a natural monument in 2005 and part of the biosphere reserve of the River Eo; low tide uncovers arches and vaults carved in the slate that reach thirty metres in height. Photo: Luis Miguel Bugallo Sánchez (Lmbuga) (CC BY-SA 3.0) What to see and do in Ribadeo