LIGO's twin detectors are separated by more than 3000 km (approximately 1865 mi.). Above, guests at the Advanced LIGO Dedication held on May 19th, 2015 gaze down one of two 4-km (2.5-mi) beam tubes of the Hanford detector in eastern Washington. The small cube-shaped building appearing to sit at the 'end' of the tube is actually the arm's 'mid station', 2 km (1.25 mi.) distant. The end station, 4 km away, is not visible.