This was a Mayan city in central Mexico know for its astranomy and observatory accessed from inside the mountain the city was built on.
the cave that leads to the observatory where the sun, during different times of the year, would shine in throught a small hole on certain locations marked on the ground. The suns location would indicated upcoming solstaces, seasons, planting and harvesting dates and eclipses.
This field is where the Mayans would play a game that required teams to hit a rubber "dodgeball-sized" ball into a hoop high on the wall using only their hips and fore arms. The WINNER of the game would be sacraficed on the spot...as in like, the center of the field....to the gods as an honor.