Rob travels to Bangor in North Wales, where he explores a lost line that was built in 1801 to transport Welsh slate from the local quarry, which once was the largest in the world, and now provides the backdrop for the world's fastest zip line. He also follows the Victorian railway inland to Llanberis, where tourists still flock to ride a special train to the summit of Snowdon, and discovers why the heirs to the throne have been styled ‘Prince of Wales' for seven centuries.