Predicted by Albert Einstein about 100 years ago, gravitational waves are ripples in space-time caused by the movement of a celestial body with huge mass. The ripples disrupt space-time and create waves that travel at the speed of light. On February 25, 2020, Japan's first gravitational wave detector KAGRA began full-scale operation. Detectors like KAGRA enable conventional telescopes that observe visible, infrared and electromagnetic waves to be used much more effectively, and they are bringing about a new era in astronomy. An NHK film crew had a chance to take a special tour of KAGRA before operation began, and in this episode, we'll take a sneak peek at its sapphire mirrors and other high-tech equipment that give it the world's best performance.