An unclimbed mountain is a mountain peak that has yet to be climbed to the top. Determining which unclimbed peak is highest is often a matter of controversy. In some parts of the world, surveying and mapping are still unreliable. There are no comprehensive records of the routes of explorers, mountaineers, and local inhabitants. In some cases, even modern ascents by larger parties have been poorly documented and, with no universally recognized listing, the best that can be achieved in determining the world's highest unclimbed peaks is somewhat speculative. Most sources indicate that Gangkhar Puensum () on the Bhutan–China border is the tallest mountain in the world that has yet to be fully summited. Gangkhar Puensum has been off limits to climbers since 1994 when Bhutan prohibited all mountaineering above due to spiritual/religious beliefs. An unclimbed and unnamed peak in Pakistan is .
Unclimbed mountains are sometimes referred to as "virgin peaks". Many virgin peaks exist because the mountain is unreachable, due to either geographic isolation or political instability. Some mountains remain off limits due to religious beliefs of a country or region that hold such mountains as sacred and should remain inviolate. Of those, Mount Kailash, a mountain in the Ngari Prefecture, Tibet Autonomous Region of China, with an altitude of is one of the most prominent. It lies in the Kailash Range (Gangdisê Mountains) of the Transhimalaya, in the western part of the Tibetan Plateau. Mount Kailash is considered sacred in four religions: Hinduism, Buddhism, Jainism and Bon. Because of its status as a sacred mountain, it is a site of annual pilgrimage, but setting foot on the mountain's slopes and attempting to climb it is forbidden.
Additionally, since the endeavor to scale taller mountains of the world is usually a major undertaking, lesser peaks, while still very formidable, simply get less attention than the taller ones, and instead these taller peaks are summited by parties following a new route or perhaps during the winter when conditions are generally more treacherous.
Challenges in definition
Definition of a mountain
Many mountains, in addition to their highest point or peak, also have subsidiary subpeaks. Generally, the topographic prominence of a peak or subpeak, as well as the general topography, all come into consideration when determining whether such apexes are considered to be independent peaks or subpeaks. Although objective criteria have been proposed for distinguishing peaks from subpeaks, there is no widely agreed standard. In 1994, the International Climbing and Mountaineering Federation classified 82 mountain peaks in the Alps whose summits were at least above sea level and with at least of topographic prominence over any adjacent mountain pass or col, as a distinct peak.
Verification of unclimbed status
It can be difficult sometimes to determine whether or not a mountain peak has been fully summited. Long before modern mountaineering commenced in the middle of the 19th century, evidence indicates that people did indeed travel up to the summits or near to the summits of major mountain peaks. Archaeological excavations in the Andes have shown that humans traveled up to in prehistoric times. Permanent settlements as high as were established as far back as 12,000 years ago in the Andes. In the Greater Himalaya region, Lhasa, in Tibet, sitting at has been permanently occupied since the 7th century and many smaller settlements across the Greater Himalaya thrive at elevations exceeding . With humans living at high elevations for many millennia, nearby peaks to such settlements may or may not have been summited at some point in the past. However, many regions away from settlements may never have been explored, especially since some high peaks in the Greater Ranges are so remote that they were unknown to local inhabitants until they were sighted by explorers.
The world's third-tallest peak, Kangchenjunga, has been summited a number of times, but on the 1955 expedition the first climbers of the peak agreed to honor the wishes of locals and not set foot on the topmost part of the mountain. Succeeding mountaineering parties may (or may not) have followed this tradition. Similarly, Nanda Devi has also been climbed but the topmost summit was not ascended and the primary summit is now off limits to climbers. Machapuchare had only one summit attempt back in 1957 when climbers came within of the summit; Nepal then banned future attempts.