The Maya people in Central America, living on the Yucatan peninsula in Mexico, Belize, and Guatemala (where Maya languages are still spoken), created an extensive civilization which peaked around the years 1200-1450. They developed an early system of symbolic writing (“glyphs") and mathematics, using a system like ours (including the zero!) but based on the number 20 instead of 10. They did not, however, use fractions.
Their astronomy was well developed, and they noted the “zenial days" when the Sun was directly overhead (“at zenith") and a vertical stick cast no shadow. Their year had 365 days, but in the absence of leap years it slowly shifted with respect to the solstices. That year was divided into 18 named “months" of 20 days each (numbered from 0 to 19), plus the “short month" of Wayeb, whose days were considered unlucky.
Yucatan does not experience summer and winter the way middle latitudes do (e.g. Europe or most of the US), and therefore the Maya calendar was not strongly tied to the seasons the way ours is. The planet Venus received major attention, and its cycles were accurately measured by Maya astronomers. In addition the Maya also observed a “ritual year" of 260 days, consisting of 20 named “long weeks" of 13 numbered days each.