The Inferno Triathlon begins in Thun and concludes atop the Schilthorn, with the half marathon commencing separately in Lauterbrunnen. Held in August within Switzerland’s Bernese Oberland, this event has been contested since 1998. The full triathlon is a demanding mountain race covering 155 km with 5,500 meters of elevation gain: 3.1 km swimming in Lake Thun, 97 km on a road bike, 30 km on a mountain bike, and a final 25 km mountain run. The course is distributed across the region rather than centered on a single location, featuring transition areas in Oberhofen, Grindelwald, and Stechelberg, and the athlete village situated in Mürren.
The race originated from the earlier Inferno Mountain Run, following its organizers' collaboration with the Schilthorn railway to incorporate swimming and cycling segments. Initial trials with seasoned triathletes raised significant questions about the feasibility of completing the entire course. The inaugural event saw 87 participants, with severe mountain conditions necessitating a revised finish in Mürren; only 16 athletes reached the Schilthorn before this adjustment. The competition later introduced a Team Trophy, also concluding in Mürren, and provides less strenuous options in addition to the primary triathlon. Weather remains a critical factor, as cold water or storms have previously led to the swim being shortened or the race route altered. Marc Pschebizin from Germany is a notable figure in its history, having secured ten victories and multiple top-three finishes.