English: Composite 3D laser scan image of El Caracol from above. El Caracol is a round stone structure with a partially ruined domed roof that originally had a cylindrical shape; it was named Caracol (Snail) due to its internal spine that climbs up in a spiral. Narrow windows cut into the outer walls seem to have been designed in order to observe the irregular movements of Venus, which was considered to be the sun's twin and held great significance for the Maya, particularly in decisions pertaining to war. The staircase at the front of the Caracol faces 27.5 degrees north of west, perfectly in line with the northern positional extreme of Venus and producing alignments at the building's northeast and southeast corners that track both the summer and winter solstices. The Caracol is one of the oldest standing observatories in the Americas, and highlights the great importance that astrological phenomena held for the people of Chichen Itza.