Pyramid of the Sun, Teotihuacan

Third largest pyramid in the world. Its base perimeter (~920m) is within 0.1% of the Great Pyramid of Giza's perimeter — on a different continent with no known contact. Contains a tunnel system beneath it, and mica sheets imported from 3000+ km away were embedded in its structure. Mica is an excellent electrical insulator and thermal shield. The city of Teotihuacan was laid out in a precise grid encoding mathematical relationships. Nobody knows who built it — the Aztecs found it already ancient and named it 'the place where men become gods.'