Why 2012?
The picture on your left is The Temple of Kukulcan at the Chichen Itza Maya ruin site located in Mexico's Yucatan peninsula. Occupied during the Terminal and Late Classic periods of the Maya empire (roughly 600-1000 AD), Chichen Itza rose to prominence during a time when most Mayan cultures were in decline.
The Temple of Kukulcan (Kulkucan in Spanish is Quetzalcoatl) is said to be a physical embodiment of the Maya Calendar. For instance, there are 91 steps on each of the four sides of the pyramid (totaling 364) plus the top platform giving us 365 to match the days of a solar year. There are many other representations of time within the construction of the pyramid as will be pointed out later.
One of the more interesting aspects of the Kukulcan pyramid is the famous decending serpent illusion which can be seen on the summer and winter solstices. A solstice occurs when the tilt of the Earth's axis is either closest to or farthest away from the Sun. It is on these days when the Sun's apparent movement north and south through the sky appears to halt and reverse direction, signaling the changing of seasons. Soltice dates can be found here.
Some Maya decendents today believe the Serpent decends every year upon the temple however the rattles have yet to descend. As such these descendents believe according to the Mayan calendar 2012 is the year when the rattles will descend.
In addition to the Kukulcan pyramid Chichen Itza is also home to The Great Ball Court. It is at the Great Ball Court where the Maya would re-enact the creation of the world and the subsequent destruction and rebirth that followed. The game involved 6-7 players on each side competing to get a ball through a round stone carving, intertwined by stone serpents, some 10-12 meters off the ground. The captain of the winning team was honored through sacrifice as depicted on carvings surrounding the court.

