The Danes top the polls as the happiest people on earth and Neil Oliver wants to know what they have to smile about. Nick Crane investigates how the Danish made a big business out of selling bacon to Britain. Alice Roberts sets sail in a full scale replica of a Viking longship to see how these ships gave Norsemen the advantage over the English in battle. Miranda Krestovnikoff meets some unflappable red deer. On Heligoland, Mark Horton reveals how in 1947 Britain's Royal Navy blew this tiny island apart in the largest non-nuclear explosion the world had ever seen and Dick Strawbridge gets access to the construction of one of the world's largest offshore wind farms.

• Alice Roberts
• Miranda Krestovnikoff