What's 500 metres wide, costs £130 million and moved 9,110 people out of their homes in China?
Come on. You know this...
We'll give you a hint... It's the Aperture Spherical Radio Telescope (FAST for short), the world's largest radio telescope that has just been completed in the remote hills of the southwest province of Guizhou , China.
It's hoped the vast telescope - so sensitive that the authorities displaced the local population to cut down on electromagnetic interference - could pick up any radio waves given off by distant life, passing UFOs or... you know, space stuff.
It's taken a while Construction started back in 1994, with the final massive reflector panel - one of 4,450 - laid in place this weekend.
VIDEO But there's some bad news Don't get too excited about hearing any alien chatter from September though: the massive dish will take around two or three years of fine-tuning before it can start accurately listening to the stars, hoping to pick up any signals sent our way from distant civilisations.
Give it a few years and we'll probably see Hiddleston's 007 running amok around it when it's inevitably used as a future Bond lair.
(Images: Rex)