The Gate of the Sun, also known as the Gateway of the Sun (in older literature simply called "(great) monolithic Gateway of Ak-kapana", is a monolithic gateway at the site of Tiahuanaco by the Tiwanaku culture, an Andean civilization of Bolivia that thrived around Lake Titicaca in the Andes of western South America around 500-950 AD.

Tiwanaku is located near Lake Titicaca at about 12,549.2 ft (3,825.0 m) above sea level near La Paz, Bolivia. The Gate of the Sun is approximately 9.8 ft (3.0 m) tall and 13 ft (4.0 m) wide, and was carved from a single piece of stone. Its weight is estimated to be 10 tons. When rediscovered by European explorers in the mid-19th century, the megalith was lying horizontally and had a large crack through it. It presently stands in the location where it was found, although it is believed that this is not its original site, which remains uncertain.

Some elements of Tiwanaku iconography spread throughout Peru and parts of Bolivia. Although there have been various modern interpretations of the mysterious inscriptions found on the object, the carvings that decorate the gate are believed to possess astronomical and/or astrological significance and may have served a calendrical purpose. In addition, scholars suggest that the design below the central figure is meant to represent celestial cycles. Being a later monument to the site in which it stands, the Gateway of the Sun could have also represented a transition from lunar religion to a solar religion based on its positioning to the sun to the West.