river cruise, arribes del duero natural park, spain

river cruise boat riverbed water valley eroded mediterranean path walk trekking route walking tour mountain ravine canyon gorge dedile geology geopark geomorphology scrub forest variegated foliage silence landscape nature wildlife environment biosphere tourism ecotourism tranquil scene view scenery tranquility conservancy beauty spa sac bioreserve natural park conservation area arribes duero salamanca castile leon spain europe