According to Wikipedia, Laser Interferometer Gravitational-Wave Observatory (LIGO) is a large-scale physics experiment and observatory to detect cosmic gravitational waves and to develop gravitational-wave observations as an astronomical tool.
Instead of the present 2-dimensional structure with 4-km beam lines on the X-axis and Y-axis, a 4-km beam line on the Z-axis could be added by tunnelling a vertical underground shaft in order to increase resolution, sensitivity and directionality of the interferometer.
