The team examines the deepest shaft discovered in the UK: Titan; they hope a 3D scan can reveal its true size and secrets about its formation.

The team learns more about the Rock's caves and tunnels; at Gorham's Cave, secrets are revealed about Neanderthal cousins and their importance to the Ancient Greeks.

An adventure into Slovenia's largest ice cave; the team scans the volume of ice, providing data for scientists to assess climate change.

The team discovers why the Maya Civilization vanished; Professor Holley Moyes reveals how a drought caused the Maya to venture underground to make human sacrifices as they prayed for rains.

Uncovering the secrets of China's giant caves; a team maps Cloud Ladder Hall, showing how its size creates an underground weather system.