Lubaantun (pronounced /lubaːnˈtun/; also Lubaantún in Spanish orthography) is a pre-Columbian ruined city of the Maya civilization in southern Belize, Central America. Lubaantun is in Belize's Toledo District, about 42 kilometres (26 mi) northwest of Punta Gorda, and approximately 3.2 kilometres (2 mi) from the village of San Pedro Columbia, at an elevation of 61 metres (200 ft) feet above mean sea level. One of the most distinguishing features of Lubaantun is the large collection of miniature ceramic objects found on site; these detailed constructs are thought to have been charmstones or ritual-accompanying accoutrements.

The city dates from the Maya Classic era, flourishing from the AD 730s to the 890s, and seems to have been completely abandoned soon after. The architecture is somewhat unusual from typical Classical central lowlands Maya sites. Lubaantun's structures are mostly built of large stone blocks laid with no mortar, primarily black slate rather than the limestone typical of the region. Several structures have distinctive "in-and-out masonry"; each tier is built with a batter, every second course projecting slightly beyond the course below it. Corners of the step-pyramids are usually rounded, and lack stone structures atop the pyramids; presumably some had structures of perishable materials in ancient times.

The centre of the site is on a large artificially raised platform between two small rivers; it has often been noted that the situation is well-suited to military defence. The ancient name of the site is currently unknown; "Lubaantun" is a modern Maya name meaning "place of fallen stones".

At the start of the 20th century inhabitants of various Kekchi and Mopan Maya villages in the area mentioned the large ruins to inhabitants of Punta Gorda. Dr. Thomas Gann came to investigate the site in 1903, and published two reports about the ruins in 1905.

The next expedition was led by R. E. Merwin of Harvard University's Peabody Museum in 1915 who cleared the site of vegetation, made a more detailed map, took measurements and photographs, and made minor excavations. Of note Merwin discovered one of the site's three courts for playing the Mesoamerican ballgame, which had stone markers with hieroglyphic texts and depictions of the ballgame.

In 1924 Gann revisited the ruins, and then led adventurer F.A. Mitchell-Hedges to the site. In his typically sensationalistic fashion, Mitchell-Hedges published an article in the Illustrated London News claiming to have "discovered" the site. Gann made a new map of the site. The following year Mitchell-Hedges returned to Lubaantun as a reporter for the Illustrated London News, accompanied by his companion Lady Richmond Brown. Anna Mitchell-Hedges, the adoptive daughter of F. A. Mitchell-Hedges, would later claim that she not only accompanied her father on the expedition, but also that it was she who found the (in)famous crystal skull there. But there is no evidence that Anna was ever in Belize, and if the skull actually had been excavated at Lubaantun it would be hard to explain why none of the official reports mention it, why other expedition members deny that it was found there, and why the publicity-loving Mitchell-Hedges did not publish even a single mention of the skull before the 1950s. According to Nickell, there is a plethora of mystery surrounding the crystal skull allegedly found at Lubaantun. New Age believers assert that there are thirteen crystal skulls that when brought together will unite humanity and heal the world. There is little evidence to suggest that the skulls have any mystical or psychic properties other than anecdotal evidence presented by Anna Mitchell-Hedges. She claimed that the skull was the secret to her longevity, and that it has the ability to kill whoever dares mock its power. Moreover, some scholars believe that the skulls may be Aztec but assert that they certainly are not Pre-Columbian or the 3,000 years old as postulated by F.A. Mitchell-Hedges. Additionally, many archaeologists postulate that most, if not all, of the skulls are European forgeries.

More importantly, it is clear from investigations by Joe Nickell and Norman Hammond that the skull was not found at Lubaantun at all, but was actually purchased by Mitchell-Hedges at a Sotheby's auction in 1943. The skull had previously belonged to the collector Sydney Burney, and photographs of it had been published in the journal Man as early as 1936.

Geoffrey Laws, along with T.A. Joyce and Mitchell-Hedges surveyed the site of Lubaantun. He noted that the site lies upon the line dividing these two geographical units, situated near the village of San Pedro Colombia, at the head of canoe navigation on the Colombia River. The ruins are located in the area formed by the convergence of two small tributaries of this river. His reports, along with other scholars, are consistent in their prostrations that the Lubaantun Maya rigorously utilized water transport. Moreover, Laws commented on the climate as being warm and humid. His report also notes an absence of any “indigenous populations” in his 1928 survey; consistent with other fieldwork at the time.