Da Dia Reef is a unique geological formation located in Vietnam, specifically in Phu Yen Province. It is known for its stunning hexagonal basalt columns, which were formed by volcanic activity millions of years ago. The reef stretches along the coastline and is surrounded by clear blue waters, making it a popular destination for tourists and nature enthusiasts. The area is rich in marine biodiversity, offering opportunities for activities like snorkeling and diving. Visitors can explore the vibrant underwater life and enjoy the scenic views of the rugged coastline. Da Dia Reef is also recognized as a national heritage site, highlighting its ecological and geological significance.