In the 1960's more than a thousand men battled seemingly insurmountable odds to build the biggest ever construction project - a hydroelectric power station. Thirty years later, a team of brave men is again attempting to overcome the extreme challenges to build another tunnel parallel to the existing one. Manapouri - The Toughest Tunnel is a compelling techno-tale of courage, tragedy, brilliance and hard, hard work and follows the highs and lows of the project from start to finish.