6. Bornholm Backyard Ultra

Bornholm Backyard Ultra uses a 6.7 km marked loop on established trails near Klemensker, on the Danish island of Bornholm. A new loop begins each hour; participants must complete the current loop and return to the start line before the next hour begins. The race concludes when only one runner is left, who must then complete one final loop solo to win. The event also features a Fun Run, limited to six loops, six hours, and 40.2 km.