If I remember correctly it is in the NY backlot section of MGM. It is a pole with an umbrella over it and if you hold on to the pole it starts to rain so that you can recreate that scene from Singing in the Rain.
It's in the Backlot area of MGM studios. It's attached to a lightpole and when you're under it, you can trigger the rain showers while you stay dry under the umbrella!
I saw Debbie Reynolds in concert this year and she played scenes (on a video screen) from when she starred in "Singin' in the Rain".
She was 19-20 years old when she made that film (1952 release)!
And she still sings and dances and puts on a VERY entertaining show.
(She says she NOW tells people who she is by saying she's "Princess Leia's Mom").