A labyrinth of tunnels underneath a tiny French village which contains mysteries from several historical eras, and a Welsh slate mine that has been given a new lease of life.
Incredible feats of human endeavour, revealing what people have built, where, how and why.
A look at some of Switzerland's 300,000 subterranean bunkers built across history.
An underground city beneath a forest in Northern France built to house 3,000 people.
The underground bases built by the German army during the occupation of Jersey.
The secrets of the largest subterranean fortress along France's border with Germany.
The military headquarters built beneath Dover Castle during the Second World War.
Description: This series looks at just some of the buildings that were designed to fight Hitler.; Category: Military & War; 8 episodes available.
Description: Tim Dunn explores the stunning architecture that lines the railway network.; Category: Engineering; 40 episodes available.
Description: Guy builds a working replica of a WWI tank and drives it at a Remembrance Day parade.; Category: Factual Entertainment; 1 episode available.
Description: The history enthusiast honours Lancaster bomber crews of the Second World War.; Category: Military & War; 1 episode available.
Description: Guy Martin recreates technical achievements of the 19th century.; Category: Engineering; 6 episodes available.
Description: Guy joins the two-year restoration of a Spitfire that was buried in a French beach.; Category: Engineering; 1 episode available.
Description: David Jason offers insights into modern British spy history.; Category: History; 3 episodes available.
Description: An archaeologist's explorations take her to an old temple - is it Cleopatra's lost tomb?; Category: History; 1 episode available.
Description: The story of the de facto Queen of England and Ireland for nine days in 1553.; Category: History; 3 episodes available.
Description: A behind-the-scenes look at the North York Moors Railway.; Category: Factual Entertainment; 9 episodes available.
Description: Investigating the most notorious murders ever to take place on the British railways.; Category: History; 6 episodes available.
Description: Shipwrecks worldwide are waiting to be discovered and have their secrets revealed.; Category: History; 6 episodes available.