Pyramid of the Niches (El Tajín)
Veracruz, Mexico
Step pyramid. Height: 20 m. Date: 8th century CE; the city flourished between 600 and 1200 CE.
Ritual building: the deep niches evoke caves, regarded as passages to the underworld. It has seven levels and 365 niches on the original structure; the side of the base is 35 m according to Wikipedia and 26 m according to World History Encyclopedia.