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Various towns across Kokořínsko and Máchův kraj, Liberec Region, Czech Republic
Čertovská výzva 666 is an eight-stage, 666 km multi-day trail challenge held across the Kokořínsko and Máchův kraj region in the Czech Republic. The event combines long-distance mountain and terrain running through forests, rocks, mines and historic sites, and is offered for individuals or as relay teams. The format is explicitly staged over multiple days and linked to a wider series of Čertovskej ultratrail races and partner towns across the Liberec Region.
The race is part of the UTMB Index Race programme and carries ITRA points for the longer formats, with the full challenge (and some extended options) awarding the highest points listed on the official pages. Registration for the main 6 June 2026 finish was reported as sold out on the organiser site, though organisers note that individual stages remain available for separate registration and that occasional places may be released. The series is organised by the Čertovskej ultratrail brand with local municipal and national partners supporting route access and logistics.
