Beside the mentioned laboratories in the US, Italy and Japan, there is another one in Germany albeit of much smaller size [0]. The length of its arms are only 6

Beside the mentioned laboratories in the US, Italy and Japan, there is another one in Germany albeit of much smaller size [0]. The length of its arms are only 600m (1/3mi) each but it serves as testbed for technologies [1] that might later be used for other observatories. [0] https://www.geo600.org/ https://www.geo600.org/ , https://en.wikipedia.org/wiki/GEO600 https://en.wikipedia.org/wiki/GEO600 [1] https://en.wikipedia.org/wiki/GEO600#Advanced https://en.wikipedia.org/wiki/GEO600#Advanced