As Heyerdahl (4) has convincingly written about the connections between Tiahuanaco and Easter Island, and as I happen to have read Posnansky with his incredibly good drawings of the Gate of the Sun, I should take the opportunity here to show the 'nut' in that environment. But the way to get there is not short; first a schematic picture of this solar observatory:

By observing where on the horizon the sun is rising (or going down) the time of the year can be determined. Central line shows where the sun will be at the equinoxes.