Just hiked Fujisan last night! I hike in the Cascade Mountains outside of Seattle about once a week and stay quite fit, and I’ve gotta say this was harder than I expected. I really liked the challenge though. The altitude makes a big difference, but I was sure to take several small breaks, especially when feeling light headed, and didn’t get sick at all. It was SO cold, especially around 2am with the wind blowing. I did not stay in the huts after all the reviews of terrible sleep, and I was fine - but it may have been nice to get out of the cold and refresh for a couple hours, even without the sleep. If you’re not staying in the huts, know that there is nowhere to take reprieve from the cold and wind so prepare to be out in it for the entirety of your hike. For some reason, I had the misconception there would be somewhere to sit inside and have a meal or coffee. but not true unless you are an overnight hit guest. Overall, I’m glad I did it. But it will take some years before I’m willing to do it again :)