The Isthmus of Kra is located in the Malay Peninsula. It lies between the Ranong and Chumphon provinces of Southern Thailand. It is bordered by the Gulf of Thailand in the east and the Andaman Sea in the west.
Andros island in the Bahamas has the largest collection of the blue holes. Andros is the largest island in the Bahamas and it more than 200 Blue Holes. Blue Holes are usually sink holes or underwater caves in shape of a circle.