Part of the 1st International Winter Mountain Running Festival on Mount Hymettus's eastern slopes (18-20 December 2026), co-organized with the Municipality of Paiania and the Hymettus Protection and Development Association (ΣΠΑΥ). Route named after Kallias, an ancient athlete said to have excelled in pankration, part of whose statue was found on Hymettus's eastern slopes in the Paiania area. Official start/finish: Central Zoodochos Pigi Square, Paiania. Confirmed start time 08:30 (the exact race day within the 18-20 Dec window has not yet been finalized). Loop course, 37km, D+2,180m, 10-hour overall cutoff. Entry requires age 18+ and, in the last two years (1 Jan 2024 to registration close), either one finish in a mountain race of 25km+ with D+1,500m+, or two finishes in mountain races of 20km+ with D+1,000m+ each (qualifying race(s), date and result link must be declared; ITRA profile link if available); individual entries only. Mandatory gear: offline GPX loaded on watch or phone, thermal long-sleeve top, waterproof/windproof jacket, gloves, and a charged phone with the race's emergency number saved; poles allowed; gear is checked before bib pickup, with random checks during the race. Checkpoints: CP1 Agios Ioannis 10km (D+600, cut-off 2h30), CP2 Kaisariani firewatch/"Kalopoula" ~20.5km (D+1,400, cut-off 5h45), CP3 Ymittos Antennas 28km (D+2,050, cut-off 8h30), finish in Paiania (D+2,180, cut-off 10h). Semi-autonomous race: carry at least 0.5L fluid and a reusable cup (no disposable cups provided). Course-cutting, outside transport or skipping a checkpoint means disqualification. DNF: hand the bib to the sweep team or nearest station staff, or make your own way back to the nearest checkpoint/Paiania and notify organizers. NSAIDs (e.g. ibuprofen) are banned during the race. Awards: finisher medal for valid finishes within cutoff; top 3 men and top 3 women overall; age categories 18-29 through 70+ need at least 6 entrants to be awarded (otherwise only the category's top man/woman), no double podium. Entry fee and cancellation terms not yet published. Info: gthathens100@gmail.com; Facebook: facebook.com/share/1GZgWNU8N9.