For more than 1,200 years, the city of Calakmul was an integral part of the Mayan world. Today, the site is located within the state of Campeche on more than 7,000 acres of World Heritage property within the Calakmul Biosphere Reserve.
The entire site is shrouded in a thick, tropical forest – the second-largest tropical forest in the Americas after the Amazon. In fact, the jungle is so thick that Calakmul remained unexplored and untouched for centuries. It only became a World Heritage site in 1993.
At its height, around the 6th century, approximately 65,000 people lived in the city. Its biggest rival was Tikal, just across the border in Guatemala.
The most important structure at the site is The Great Pyramid, whose base spans five acres and whose peak rises 174 feet. It is the tallest pyramid in the Yucatan and, yes, you can still climb it.
Fun fact: On a clear day climbers can see the neighboring site of El Mirador in Guatemala.