⏵ Course guide · Northern Wisconsin
The Underdown Trail Races run remote, glacier-formed singletrack through the Underdown Recreation Area near Merrill, Wisconsin, grassroots and unapologetic about the challenge since 1989. I will walk you through the terrain and what the race itself warns you about first, then give you a pacing and fueling plan built for a genuinely backcountry effort. There are free calculators along the way to dial in your own numbers.
These facts come from the official race page. Check the current year details, including cutoffs, before you commit. Race logistics can change year to year.
This is grassroots backcountry trail running, and the race does not dress it up as anything else.
The course runs primarily on singletrack shaped by glaciers thousands of years ago, climbing hills the race says number up to 75, passing isolated lakes along the way. Dozens of boardwalks cross the wetter sections, a real feature of running through this kind of terrain rather than a minor inconvenience.
The organizers are unusually direct: cell phone service will be spotty, the course goes through remote areas, and you should be comfortable being alone in the woods before signing up. That is not marketing language, it is a genuine logistics consideration for how you plan crew, communication, and your own mental preparation.
The 60K, Marathon, and Half Marathon all run on the same challenging singletrack. If this is your first time at Underdown, the race itself suggests starting with a shorter distance before stepping up to the 60K, a genuinely useful piece of race-specific advice worth taking seriously.
With up to 75 hills on course and genuinely remote stretches, pace by effort and terrain, not by a number you picked before seeing the trail.
Seventy-five hills, even modest ones, add up to real cumulative fatigue over a 60K. Run the climbs at a controlled effort early rather than treating each one as an isolated obstacle, since it is the accumulation across the whole course that will decide your back half.
With spotty cell service and long remote stretches, carry what you would need to be self-sufficient for longer than usual between aid points, and let someone know your expected pace and finish window. This is not a course where a quick phone call solves an unexpected problem.
⏵ Free tools to plan your effort
Stocked aid stations and drop bag transport are provided, but exact spacing is not published, so plan to be self-sufficient between them.
Aim for roughly 40 to 70 grams of carbohydrate per hour for the 60K, and carry more fluid and calories than you think you need given the long, remote stretches between aid. Use your drop bag to reset your carried supply rather than assuming frequent resupply.
Aim for sodium in the 400 to 700 mg per liter range, adjusted upward if the day runs warm and humid, common for mid-August in Northern Wisconsin. Boardwalks and lake-adjacent sections can mean higher humidity even when the temperature itself is moderate.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your pace, and a mid-August Wisconsin day with the free ultra fueling calculator. Browse the rest of the free running tools at the tools hub.
⏵ Train for it with Summit Line
Get a training plan built around YOUR fitness and the hill-heavy, remote singletrack this course demands. Summit Line reads your real training, builds the climbing durability 75 hills asks for, and rehearses your fueling so race day is something you execute, not guess at.
The race runs primarily on singletrack through the Underdown Recreation Area, terrain the organizers describe as "formed from glaciers that swept the area thousands of years ago." Expect hills, up to 75 of them by the race's own count, isolated lakes, and dozens of boardwalks crossing wet ground along the way. This is backcountry trail running, not a manicured park loop.
Genuinely remote. The race is direct about it in its own warnings: cell phone service will be spotty, the course goes through remote areas, and you should be comfortable being alone in the woods before signing up. If you are new to trail ultras, the race itself recommends starting with one of its shorter distances rather than jumping straight into the 60K.
The official race page I checked does not publish specific cutoff times. A detailed racer guide with rules and schedule is referenced on the site (a 2025 edition was linked pending the 2026 release), so check that document, or contact IRONBULL directly, for the current year's cutoffs before race day.
The race does not soften this: it describes the event as "meant to be a physical and mental test" on "challenging trails," and specifically warns that newer trail runners should try a shorter distance first. Between the hill count, the remote singletrack, and the boardwalk crossings, treat the 60K as a genuine backcountry test, not an entry-level ultra.
By the race's own recommendation, probably not as your very first trail ultra. The remoteness, the singletrack technicality, and the sheer number of hills push this toward runners who already have some trail experience and are comfortable being alone on course for long stretches. If this is your first Underdown event, the race suggests starting with a shorter distance before the 60K.
Finishers receive a custom, commemorative Underdown mug, along with divisional awards. The event also includes stocked aid stations, drop bag transport, and a post-race party with live music, food, and beer, a genuinely grassroots celebration for an event that has been "rowdy since 1989."
Link this guide
Race directors and clubs: link or embed this guide anywhere. It stays current.
<a href="https://runsummitline.com/guides/underdown-trail-races">The Underdown Trail Races course guide</a><iframe src="https://runsummitline.com/embed/race/underdown-trail-races" style="width:100%;max-width:420px;height:180px;border:0;" loading="lazy" title="Underdown Trail Races course guide by Summit Line"></iframe>This guide is independent and for planning only. The course, cutoffs, and dates come from public sources and can change year to year, so confirm the current specifics with the official race before you register or run. The fueling and pacing advice is general and not medical advice.
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