After more than two decades of drilling, Russian scientists report they have reached the surface of a freshwater lake in eastern Antarctica.
More than 300 subglacial lakes are known to exist on the Antarctic continent, but this is the first time one has been reached.
Lake Vostok is buried beneath nearly 4km of ice. It has been sealed for nearly 20 million years.
Researchers hope it may contain lifeforms new to science.
The lake's location is one of the most inhospitable places on Earth. It is where thermometers recorded the lowest ever temperature on the planet, -89 degrees Celsius in July 1983.
Vostok Station was first set up in 1956. However, it was only in the 1970s when, with the help of radar, British scientists first started to suspect there might be something underneath all the ice.
Further geophysical survey data then established its true scale.
With an area of 15,000 square km and more than 800 metres deep, Lake Vostok is similar in size to Lake Baikal in Siberia or Lake Ontario in North America.