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. 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. 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, will 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