It appears only in The Enchantress.
The Pyramid of the Sun is nearly one and a half miles long and stands almost a mile high. It is depicted as ten times as long as the Pyramid of Giza, which is seven hundred and fifty-six feet in length. The original pyramid was bigger.
The Pyramid of the Sun is and enormous flat-topped, stepped pyramid. It is described as "surrounded by a vast golden plane, which was in turn encircled by a ring of water. Canals radiated from the circle like spokes on a wheel." It is also hollow. Like many things, The Pyramid of the Sun is made of golden rock.
The original Pyramid of the Sun was built the Great Elders who tore Danu Talis from the seabed. The original was bigger, but the second Pyramid is still viewed as huge. The previous Great Elders and Elders, though rarely, gathered in the Pyramid for councils and important hearings and courts.
The way the Pyramid is positioned and built with gold stones and layers of silver, renders all auras inside the Pyramid useless, also draining them from the beings inside. All this power is then funneled to the top of the Pyramid. This is another important part of Osiris's and Isis's plan with the twins.
Soon after the twins are left to wait, they are attacked by three Bear-sarks sent by Anubis to kill them. There is a brief fight that is soon ended by Tsagaglalal. She then brings the twins to the top of the Pyramid and left them, so that they could do the right thing alone, as it said in The Codex.
Afterwards, the battle of Danu Talis takes place on the pyramid.