Mount Myōboku.
After Naruto arrived, he immediately began training in Sage Mode, starting with theoretical knowledge, followed by the experiences of Jiraiya, Sage Fukasaku, Sage Shima, and the other seniors.
Back at the Ninja Academy, Naruto had never cared for theoretical knowledge and had never seriously studied it. But under the immense pressure he now faced, he focused completely and quickly grasped the principles of Sage Mode.
After two days of preparation, Naruto stepped up personally and officially began training in Sage Mode!
Sage Fukasaku and Sage Shima stood on Jiraiya's shoulders, both looking rather unconcerned.
In their view, mastering Sage Mode in such a short time was absolutely impossible.
Furthermore, Naruto was Minato Namikaze's son. They still remembered how Minato Namikaze had often stumbled through his own Sage Mode training, which only made them feel that Naruto and Jiraiya were wasting their time.
Another two days passed, and Sage Shima and Sage Fukasaku left.
Three days later, even Jiraiya ran out of patience and went to peep on the female toads bathing.
After they had all left, Naruto continued cultivating in peace.
Because he had already reconciled with the Nine-Tails, the training process was exceptionally quiet, and nothing external could affect Naruto.
Five more days passed like this before Naruto finally made a breakthrough.
He sensed the Natural Energy that existed everywhere beyond his body. It was an energy utterly different from Chakra, even stronger than the Nine-Tails' Chakra. Unfortunately, although Naruto could sense Natural Energy, he was still unable to wield it.
He opened his eyes, only to find that Jiraiya, Sage Fukasaku, and Sage Shima were all gone.
After giving it some thought, Naruto immediately formed Hand Seals and summoned a Gamakichi, then had him call Jiraiya over.
When Jiraiya arrived, his face was bruised and swollen.