Mount Sagiri

Mount Sagiri is a huge mountain in a mostly unpopulated region. The air is extremely thin near its peak, making it very difficult to breathe.

History
The mountain is used by Sakonji Urokodaki to train children working towards becoming a Demon Slayer. Sakonji tests his students by giving them the task of slicing a boulder using a katana. If they succeed, they are sent to participate in the Final Selection. Children who complete the Final Selection are accepted as Demon Slayers. For those who die in the Final Selection, their spirits return to the mountain.