Blue Hole

Blue Hole is a well-known cavern dive site in Palau, formed by four natural openings in the reef plate at around 1–2 metres depth on the reef top. The four holes connect into a single chamber below, with a spacious domed ceiling at approximately 20 metres and an arched exit — known as the Archway — opening toward the outer wall at 25–30 metres depth, with a maximum depth of 30 metres.

At midday, sunlight pours through the four overhead openings in dramatic shafts, illuminating the cave interior against the dark water. The ceiling of the cave is home to Southern Grouper, Collins' Angelfish, Capoeira, and juvenile Triggerfish, while lionfish and jack fish are also seen hanging near the roof. Entry is possible during high tide, when divers can drop vertically through one of the openings directly from the surface; the site is reached by boat.

Conditions inside the cave are calm with no current, and visibility runs 15–20 metres or more. The site is recommended for Advanced Open Water divers due to the enclosed cave environment, the depth of the Archway, and the risk of decompression; the narrow cave openings are an additional hazard to be aware of.