The 6h-Klosterseelauf is a six-hour loop race in Triefenstein-Trennfeld, Germany, run around the Klostersee. Runners start and finish at the Fischerhutte, then continue covering the same paved 1.81 km circuit for as much distance as they can within the time limit. It is a road race, but the format places it closer to ultrarunning than a standard fixed-distance event, as the result is measured by total distance rather than by finish time.
Each lap includes about 10 metres of climb and descent, making the course short, repeatable, and easy to manage for pacing, aid, and counting laps. RST Lauftreff Marktheidenfeld organizes the race, with a field cap of 300 runners. The event is open to all but also attracts ultra runners, with past results showing distances over 63 km. Its distinct tradition is the charity component: it supports Kinderhospiz Sternenzelt in the Mainfranken area, with a portion of the entry fee donated and an additional donation made for every lap completed.