Sasuke tells Naruto and maybe other people about it. Naruto follows Sasuke to train there. But between both of their missions they don't train there all that often. Naruto also needs Sasuke to even access Kaguya's dimensions, so he can't train by himself there. By the time The Last happens Naruto beats Toneri easier. After that Naruto is too focused on his relationship with Hinata, studying and preparing himself to be the Hokage at some point, and his other missions to really commit to training there. (At this point only Naruto and Sasuke knows about it.)
Meanwhile Sasuke, as the sigma giga chad he is spent a lot of his time training there whenever he isn't needed to deal with some Otsutsuki related investigations or any mission that requires his help. At this point, Sasuke greatly surpasses Naruto. He managed to increase his Chakra capacity significantly, so now he can use more of his Rinnegan abilities. "I can make my own prosthetic arm, neat." Sasuke thought as he tested the Asura path abilities. Also thanks to this and better mastery of his Rinnegan he can travel between dimensions more freely, and now can teleport more people with him.
During Sakura Hiden, Sasuke suddenly appeared and annihilated Kido when he tried to imitate him and "confess his love" to Sakura. He then went back to training after poking Sakura's head.
At the day Naruto finally becomes Hokage, he isn't completely one-tapped by Himawari, and managed to recover from the Gentle Fist technique once Hinata helped him. Sometime later, he told Katasuke about his absolutely and totally original completely brand new idea of training Shinobis in a place with high gravity to enhance their growth speed. He tasked Katasuke to research on the effects of high-gravity training on Shinobi and if it's feasible to make a dedicated high-gravity chamber for high intensity training. Rock Lee and Might Guy (who now has a proper prosthetic leg because plot) burst into the Hokage office upon hearing about this, pleading Naruto to allow them to volunteer on that project. Naruto allows it, even paid them for it.
Months later, the gravity chamber is done. With Lee and Guy spending nearly all their free time training there, they absolutely loved that chamber. Kakashi sometimes also tagged along with them. Katasuke built a few more of them, and Naruto opened those chambers to the public. Another one is built under the Hokage office for Naruto's personal use.
