The Merkerser Kristallmarathon is one of the most unique running experiences in Europe—staged entirely underground in the Erlebnisbergwerk Merkers, near Eisenach, Germany. At 500 meters below the earth’s surface, athletes race in constant conditions of 21°C, making it a winter marathon unlike any other. The marathon covers 13 laps of a 3.25 km course through the illuminated mining tunnels, while the half marathon is reached after seven laps.<br><br>Participation is capped at 750 runners, ensuring an intimate yet atmospheric race deep in the salt mine’s crystal chambers. Strict cutoffs apply: runners must complete 12 laps (39 km) within 4 hours and 45 minutes to continue. Those stopping earlier between laps 7 and 12 will be recorded in the half marathon results, outside of official competition. More than just a test of endurance, the Kristallmarathon is a surreal adventure in one of Germany’s most extraordinary sporting venues.