The Brick Experiment Channel posts videos about doing interesting things with Lego bricks. Last year they made a gear train with 186 Lego gears. The motor spun at 375 RPM. Each gear reduced the RPM. The fourth gear spun at 1 RPM. The final gear ratio was 1.034 googol:1.
The latest video goes in the opposite direction. They use gears to see how fast they can make a wheel spin from hand power only. They did a good job, reaching over 19,000 RPM.