Mazarrón is a municipality in the autonomous community and province of Murcia, southeastern Spain. The municipality has an area of 318.7 square kilometres (123.1 sq mi), and a population of 31,562 inhabitants in 2019. A military fort (named C1 or Castillitos-small castles) built between 1930 and 1936 during the reign of Alfonso XIII of Spain and the Second Spanish Republic exists as a tourist attraction on the old road between Mazarrón and Cartagena, and although it is accessible from the Bay of Mazarrón it is not in the municipality itself.

The Bay of Mazarrón is sheltered by the last foothills of the Sierra de la Almenara, a mining area since the Carthaginian era. Over 35 km of beaches, unspoiled coves and rocky sea beds. Due to the nature of the surrounding rocks, however, the beach at Bolnuevo is of coarse grit, as are most of the beaches along this part of the coast.

The Torre de los Caballos on Los Caballos peak were built for the town's protection against pirates from the mid-16th to the early 18th centuries.

The economic development of the early 20th century led to the construction of emblematic buildings in the style known as Murcian Modernism, including the Mazarrón Town Hall and the former Cultural Athenaeum.

The guns in Cartagena were built to defend the vital port of Cartagena in the 20th century, these guns alongside the fort and other coastal defences, stand 56 feet long, weighing a total of 88 tons each and being able to fire at a range of some 20 miles.