Explorer Steve Backshall travels deep into the Yucatan, Mexico, on the trail of the ancient Maya. His team – including Mexican archaeologist Guillermo de Anda, pioneering cave diver Robbie Schmittner and former Royal Marine Aldo Kane – want to explore secret caves the Maya called Xibalba, or the 'place of fear'. The ancient Maya believed the caves were a portal to a supernatural underworld, a place full of hellish terrors. It’s a mission that brings Steve face to face with the macabre secrets of this ancient civilisation.

In the first cave they explore, the walls are covered in sinister handprints - some from children as young as two years old. But what happened to them? Abseiling in full dive kit, they lower themselves into the darkness of the next cavern. They come across a flooded graveyard full of human remains – all left as offerings to the gods. It’s a place where humans were probably sacrificed, and it's a chilling insight into the cruelty of the ancient Maya.

But as they push deeper into more caves, they discover another side to the Maya. They witness incredible artefacts that add to our understanding of why the Maya risked their lives to travel so deep into this underworld. In the final cave, they discover a hidden underwater lake. Steve and Robbie don cave-diving kit to venture deeper into it than anyone has before. Show less