Many known travel websites rate Tongariro Crossing as the best one-day hike in New Zealand. The Tongariro Alpine Crossing is roughly 20 km long and takes about 7-8 hours to complete. If you base yourself out of Taupo, the North Island's adventure capital (the northern equivalent of Queenstown, in some ways), you have access to a few tour operators offering this hike as guided tours, including transportation to and from the mountain. The Tongariro Crossing is not a circular track, meaning you will be dropped off on one side of the mountain and picked up at the other. The hike leads through varied terrain, including springs, lava flows, lots and lots of volcanic rock and the spectacular turquoise lakes.