Snorkelers swim above a blue hole on Palau's barrier reef. This hole formed when sea level was much lower than it is today.

abyss adventure backlit bay beauty in nature below biodiversity blue cave cavern cenote color image coral triangle day directly below diver ethereal exploration grotto hole horizontal illuminated lagoon leisure activity light marine biology micronesia mystery natural light ocean outdoors palau photography sea shining silhouette sinkhole snorkeling spelunking sunlight swimming tropical climate underground underwater unrecognizable person waigeo water wilderness