This is a video of the 100-gear 'Universe's largest gear reduction' built by Youtuber danielbruin. It features a 1 to 10 gear reduction repeated a hundred times so the last gear would take a googol (1 with 100 zeroes) turns of the first gear for it to rotate a single time. In his own words while I crank the handle on one of those machines that flattens a penny into a forgettable souvenir:
Today at 14:52 I will be exactly 1 billion seconds old. To celebrate I build this machine that visualizes the number googol. That's a 1 with a hundred zeros. A number that's bigger than the atoms in the known universe. This machine has a gear reduction of 1 to 10 a hundred times. In order to get the last gear to turn once you'll need to spin the first one a google amount around. Or better said you'll need more energy than the entire known universe has to do that. That boggles my mind. Whoa -- it would take more energy than in the entire known universe to turn the final gear?! Is that true? *makes phone call, gets no answer* "Stephen Hawking passed away, remember?" What! What year is it? "2020." Oh my God it worked! "What did?" Drinking myself stupid.
Keep going for the video, as well as an extended cut of the thing turning for a full hour.