Hardergrat Ridge Hike, Switzerland
The hike along the Hardergart from Interlaken to the Brienzer Rothorn might be the best hike I've ever done. It's also up there as one of the most strenuous hikes I've completed to date.
You start from the town of Interlaken hiking up to the Harder Kulm above the city from there you follow the ridge for hours and hours until you reach the Brienzer Rothorn at the other end of the Brienzer Lake. The way goes over several peaks and covers 27 kilometer and more than 3,000 vertical meters. This is all worth it however, because the views are amazing.