The most famous part of Tiwanaku is the Gate of the Sun, a huge doorway carved from a single block of stone. Carved into it are a sun god and rows of winged figures. Nobody is completely sure how the people of Tiwanaku moved such enormous blocks of stone without modern machines - some blocks weigh more than 100 tonnes.
The Tiwanaku civilisation was very clever at farming. They built raised fields separated by channels of water. The channels kept the crops from freezing at night because water holds heat better than soil. This system worked so well that modern farmers are now copying the same idea.
Tiwanaku was not just a city - it was a religious centre and the most powerful place in the whole Andes region for hundreds of years. Eventually the city was abandoned, and wind and rain slowly covered it with earth. Archaeologists are still digging it up and making new discoveries every year.
Today visitors can walk around the huge stone platforms, see giant stone statues called monoliths, and step through the Gate of the Sun. The Aymara people of Bolivia and Peru consider Tiwanaku sacred, and every year at sunrise on the Aymara New Year, thousands of people come here to celebrate.