Earth is filled with places that remain difficult for humans to reach. While mountaineers have climbed some of the planet’s highest peaks, explorers, scientists and workers have also traveled thousands of metres beneath the surface and below the ocean. From the deepest point in the Pacific Ocean to enormous underground caves and mines, these locations demonstrate the extreme environments humans have managed to investigate.
The deepest known point in Earth’s oceans is Challenger Deep, located within the Mariana Trench in the western Pacific Ocean. Its depth is more than 10,900 metres, making it deeper than Mount Everest is tall.
Humans first reached Challenger Deep on January 23, 1960, when Swiss oceanographer Jacques Piccard and U.S. Navy Lieutenant Don Walsh descended in the bathyscaphe Trieste. The vessel reached a measured depth of approximately 10,911 metres. Piccard and Walsh spent about 20 minutes on the seafloor before beginning their ascent.
More than five decades later, filmmaker and explorer James Cameron completed a solo descent to Challenger Deep in 2012. Human expeditions to the site have continued with specially designed deep-sea submersibles.
The Kola Superdeep Borehole in northwestern Russia represents a different kind of deep exploration. Unlike Challenger Deep, humans did not physically travel to its bottom. Instead, Soviet scientists drilled into Earth’s crust to investigate its geological structure.
The drilling project reached a maximum vertical depth of 12,262 metres in 1989, making it the deepest artificial point ever created in Earth’s crust. The project began in the 1960s and continued through several stages before eventually ending in the 1990s.
The borehole provided scientists with samples and information about rocks deep beneath Earth’s surface. Although it extends farther from the surface than Challenger Deep, it is important to distinguish it from places humans have physically visited.
In South Africa, humans routinely work at extraordinary depths beneath the ground. Mponeng gold mine, located in the West Wits region near Johannesburg, is recognized as the world’s deepest mine.
Current mine development reaches approximately 3,841 metres below the mine datum, while working areas extend to several kilometres underground. Official technical reports describe Mponeng as the world’s deepest mine.
The environment becomes increasingly difficult at such depths. Rock temperatures can reach around 60°C, requiring extensive cooling and ventilation systems to make underground operations possible.
Natural caves provide another route into Earth’s depths. Veryovkina Cave, located in the Arabika Massif of the Caucasus region, has been explored to a depth of 2,212 metres, according to Guinness World Records.
In March 2018, Russian speleologists reached the cave’s deepest known point during a 12-day expedition. The team also collected samples of underground organisms, including rare species adapted to life in the cave environment.
Veryovkina is one of the world’s few caves that extend more than two kilometres below their entrances. Its passages include steep shafts, underground waterways and sections that require technical climbing and specialized equipment.
These locations show that “deepest” can mean different things. Challenger Deep is the deepest known point in the ocean that humans have physically reached, while the Kola Superdeep Borehole extends farther into Earth’s crust but was explored using drilling equipment rather than human travel. Mponeng demonstrates how far humans can work underground, while Veryovkina shows the extraordinary depths accessible through natural cave systems.
Together, these places represent some of humanity’s most challenging explorations. Each requires specialized technology, careful planning and protection from extreme pressure, temperature, darkness and geological conditions. Even after reaching these depths, large portions of Earth’s deep environments remain difficult to access and study.
