World's Tiniest Electric Train Set
Allegedly the world's smallest model train, Stan's Trains' TY-Scale train is built at the scale of 1:900.
Note the tape dispenser and dime (in video) for reference.
The obsessively small scale truly demonstrates the hobbyist's technical mastery. Interested in venturing into the world of model trains? WonderHowTo has a whole slew of HowTo videos on the topic.