Where is the world's most famous laboratory for measuring the gravitational constant?

There is no single place that owns the gravitational constant, because measurements of G are repeated in precision laboratories around the world. National metrology institutes such as NIST in the United States and similar labs in Europe and Asia have all contributed to the long effort to measure it. Unlike many other constants, G is difficult to determine precisely because gravity is extremely weak compared with other fundamental forces. That makes it one of the most challenging numbers in physics to pin down.