Mind the gap! Aides panic as William and Kate make spur of the moment decision to edge along railway tracks next to a steam train that the Queen and Prince Philip travelled on nearly 60 years ago. One foot wrong and they could have been sent tumbling into the freezing water. But the Duke and Duchess of Cambridge looked fearless as they balanced precariously on the edge of a railway line, looking down at a river several feet below. After touring a steam train, the couple climbed down from the cab while it was stationed on a bridge on the White Pass and Yukon Route railway, at Carcross, Canada. Kate was left facing outwards towards a drop but quickly regained her composure and sidestepped towards solid ground, her husband following close behind. The royals made the spur-of-the-moment decision after being told the Queen and Prince Philip had travelled on the train when they visited the region in 1959. But while the Cambridges' appeared to revel in the adventure, it left their aides momentarily panic-stricken. The impromptu stop came as the royal couple made their way down picturesque Montana Mountain in the remote northwestern Canadian province of Yukon. On route, William spotted the train, puffing up clouds of smoke, and was told how his grandparents had travelled in the last carriage on their royal tour nearly 60 years ago. The over-excited prince couldn't resist taking a peek and encouraged his wife to cross a wooden bridge over scenic Lake Bennett for a closer look. Their guide, Chief Andy Carvill, 52, said: 'The Duke asked if he could go in and they got inside the train and blew the steam whistle. I told them about the Queen's coach and they were pleased to hear that.'