Overview
Round buildings are rare in Maya architecture and this one is not aligned with the rest of Chichén Itzá, but with the sky. Of the surviving window sightlines, several correspond to the northern and southern extremes of Venus, which the Maya tracked closely enough to record its cycle in the Dresden Codex. The upper chamber is ruined, so what the instrument could do is partly reconstructed from the stubs that remain.
Highlights
Stand back to the north-west to see the tower against the platform corners, which is how the alignment reads. It is on the way between El Castillo and the Nunnery group and is easy to pass at a glance. The site museum explains the Venus cycle better than the panels here do.