“Extreme Day Hike” … sounds like an exaggeration of the simple feat of walking. It is.
It all relative. For a person not in shape, an extreme day hike may be a walk around the shopping center. On the other hand, for a trail or marathon runner, these hikes may be a walk in the park. This site characterizes “The Extreme Day Hike” as one that consumes most of the day in a challenging adventure in a spectacular natural setting, typically gaining an elevation gain of 4000 feet +, 14 miles round trip, and on a trail.
Other easier day hikes are also described on this site, especially if there is a unique aspect such as exotic, exciting, scenic, or otherwise entertaining. Examples are a section of the Great Wall of China, a major city hike/walk, or my favorites: Hiking up a hill to the top of an island to 13,300 feet and looking down at an “ocean” – Lake Titicaca – at 12,500 feet.
Any hike to over 14,000 feet altitude, a “Forteener,” is clearly an an extreme day hike due to two challenging factors: Lack of oxygen and quickly changing weather. Even after acclimatization, some people do not cope well with the high altitude and become ill. Secondly, the danger of unexpected storms bringing heavy rain, snow, or thunderstorms is greater at higher altitudes.
Another version of an extreme day hike is to cobble together multiple hikes in a locale, the total distance, elevation, and interest combine to make a great experience. See the DayHiker article on the Capitol Reef National Park in the red rock country of Utah. I stitched together 3 of the parks best hikes for a fantastic long day.
Ready to see some examples?