Ninjas were Japanese spies, killers, and assassins. I would imagine their training took years to master their precisely executed stills under the cloak of darkness and all without making a sound. They had to be experts in martial arts, weaponry of all sorts, have super strength with amazing agility, and nerves of steel. And I'd add, not be squeamish about killing someone with dead accuracy.
This art form, jinjutsu, it may be called a self-defense technique of martial art precision killing has died out. The need for Ninjas is gone.
The secrets of the Ninjas was passed down from father to son, but it has come to an end.
But, no doubt, Ninjas will live on in movies, games, toys, and in contests challenging the body in every imaginable way, giving us some idea of the rigors the Ninjas executed perfectly.
FYI- More interesting stuff about Ninjas --
What a ninja did.
Some aspects of Ninja training which gave them strength, precision, self-control.
A famous Ninja.
An obstacle course testing physical strength, stamina, speed, agility, and balance. The video below shows the first female to conquer this challenge for the title, 'First Female Ninja Warrior'
Check this video of some extreme strength, like a Ninja--
and this Ninja-like training bedroom
And lastly, step-by-step, how you can be a Ninja,
The mighty Ninja will never be forgotten.