Top: the Super-Kamiokande. Bottom: the Stellarator. The former is a particle detector; the latter is a one-of-a-kind machine that can recreate the heart of a star right here on Earth. Both are in Japan, buried underground like most of the insanely gigantic scientific research machines in this list. They truly defy belief.
https://gizmodo.com/14-immense-scientific-instruments-you-wont-believe-are-1200943611