Incredibly transparent sea with the colorful sign "Holbox" in the foreground. Holbox is a beautiful island in the Mexican state of Quintana Roo, located on the north coast of the Yucatán Peninsula. It is approximately 41.84 kilometres (26 miles) long and 1.5 kilometres (0.9 miles) wide, and it is separated from the mainland by 10 km of shallow lagoon that is home to flamingos, pelicans and other rich birdlife.