Distance
Terrain
The Saroma Lake 100km Ultra Marathon Online Challenge is a virtual event that brings the spirit and camaraderie of Japan's longest-running ultramarathon to runners anywhere in the world. Participants pick a one-month or two-month window and cover a cumulative 100km at their own pace on routes of their own choosing, logging the distance on an online platform that tracks progress and shares achievements with fellow entrants. The challenge takes its character from the real Saroma Lake course in Hokkaido, which winds through picturesque landscapes of serene lakeside paths and rugged forest trails. Entry is handled through the RUNNET registration portal, with fees ranging from around 4,990 to 12,990 yen depending on the option selected, and runners connect through event social media channels to swap tips, stories and encouragement. It suits anyone who has already finished Saroma Lake in person as well as those who simply dream of doing so one day.
Inspired by Japan's longest-running ultramarathon at Saroma Lake, Hokkaido
Scenery of serene lakeside paths and rugged forest trails in the original course
Run the distance anywhere in the world on your own route
Progress tracking platform shared with a global community of runners
Start / Finish
Anywhere: this is a virtual challenge and each participant chooses their own start point
Anywhere: participants complete the 100km cumulative distance and submit their log through the online platform
What you get
Access to an online platform for logging distance and tracking progress
Connection to a global community of challenge participants through event social media channels
On the day
Other questions
It is a virtual challenge rather than a mass-start race. You enter through the RUNNET portal, choose a one-month or two-month window, and then cover a cumulative 100km at your own pace. You log the distance on the event platform so your progress counts towards the challenge total.
Anywhere you like. There is no fixed course, so participants run on local roads, trails, parks or treadmills and add the distances together. The event is inspired by the Saroma Lake course in Hokkaido, but you do not need to travel to Japan to take part.
Yes. The challenge is cumulative, so the distance you cover in each run or walk is added to your total until you reach 100km within your chosen window.
Both cover 100km in total. The one-month options (September, October, November and year end) require you to complete the distance inside a single calendar month, while the two-month options give you twice as long and are split into Stage 1 and Stage 2.
Yes. The challenge is designed for runners around the world, which is why the distances are logged remotely and the community connects through social media rather than at a single venue.
Entry fee
Registration isn't open yet. We'll show pricing when the organiser confirms.Kiryu, Japan
Expected October 2027
Provisional date, around Oct 7Are you the organiser of Saroma Lake 100km Ultra Marathon Online Challenge 2 Month 100km Stage 1 (Oct-Nov) (サロマ湖100kmウルトラマラソン オンラインチャレンジ【2month 100km Stage1（10-11月）】)?
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