At the top of El Caracol’s grand staircase is a tower, now rounded by decay, but originally in the form of one smaller cylinder stacked on a larger one. (Imagine a double-decker wedding cake.) To gain access to the uppermost tower, you have to walk through a narrow winding staircase. It is this staircase that earns the structure its name;
In the half-ruined higher tower of El Caracol, three openings survive. These three openings are small, narrow, and irregularly placed, suggesting that they are actually viewing shafts. It turns out that these windows do in fact align with important astronomical sightlines. Looking through these windows a thousand years ago, observers could have watched for Venus rising at its northern and southern extremes, as well as the equinox sunset. The three window shafts that remain in the upper tower of El Caracol seem to align with various celestial events on the horizon.