Media personnel have been allowed to visit an underground astrophysics observatory for the first time in 12 years.
Super-Kamiokande is located at a depth of 1,000 meters in Gifu Prefecture, central Japan.
Measuring 40 meters in diameter and height, the observatory detects the elementary particles called neutrinos coming from space.
It's usually filled with 50,000 tons of water, but has been drained for refurbishment.
The wall is equipped with more than 10,000 round-shaped sensors that capture the extremely weak light that neutrinos emit when they collide with water.
University of Tokyo Professor Takaaki Kajita and other scientists conducted research on neutrinos at Super-Kamiokande. Kajita was jointly awarded the Nobel Prize in Physics in 2015 for proving that neutrinos have mass.
The university says the observatory will be filled with water next month and researchers will resume their observations next year.
University of Tokyo Professor Masayuki Nakahata says scientists allowed the media to visit the site because it's a rare opportunity.
Nakahata expressed hope that Super-Kamiokande will remain the world leader in neutrino research and will help scientists to make further discoveries about the history of the universe.