KAGRA (or Kamioka Gravitational Wave Detector, formerly called the Large Scale Cryogenic Gravitational Wave Telescope or LCGT) is a gravitational-wave detector in Japan that began full operation in February 2020. It is a Michelson interferometer with 3 km arms, similar to the LIGO detectors and Virgo. As a fourth such detector, more data will be collected on each GW detection, which (among other things) will assist in determining the direction of the event's source. It is entirely underground, installed in an enlarged mine, and it uses cryogenic mirrors to help reduce noise, specifically mirrors made of sapphire, which along with their suspension mounting will be kept at 20 K during operation. It aims for a sensitivity capable of detecting two to three events a year. Tunnel excavation was completed in 2014, the detector began test operation (without the cryogenic cooling) in 2016, and installation of the fully-sensitive (cryogenic) instrument was completed in October 2019.