Japan's seasons are more extreme than anywhere else on the planet, and has deeply influenced its people and culture. Autumn is no exception.
Kansai is the second-most populated region in Japan, centered Osaka and Kyoto. This region, and particularly Kyoto, is well renowned for its beautiful architecture, but combine that with Japanese maple trees and it's as sublime as it gets.
Kyoto is the best hub for experiencing autumn in Kansai. I headed into Kyoto City in the 3rd week of November and stayed in the Kyoto Prefecture until the end of November. The first site I headed to was Mt. Takao, which is earliest to peak given its altitude. It's daytrippable from Kyoto, but worth staying the night. Unfortunately, you have to book months in advance for the very limited accommodation that's available. The rest of Kyoto Prefecture is more expensive than usual too, but there are plenty of options.
The other day trips I went on from Kyoto were Kameoka, Amanohashidate, Arashiyama, Ohara, and Nara. All of these are also daytrippable, but Amanohashidate especially is much better done with a night's stay.
Within the Kyoto urban area itself, I shortlisted about 50 autumn sites. There are over 2,000 religious and historic sites in Kyoto, after all! The depth and breadth of this city's beauty is like no other I've ever visited. I couldn't get to all of them, but covered all the essentials, plus many smaller sites. It took me over 10 days for all of that - though I do like taking my time, and mostly improvise. Particularly given autumn foliage is a dynamic beast, being flexible helps. My favourites from the Kyoto urban area were: Tofukuji, Kiyomizudera, Enkoji, Nanzenji, Eikando, Tofukuji, and Bishamondo. (Speaking strictly in terms of autumn, of course.)
Kyoto does get extremely crowded during peak autumn, but it's mostly just the handful of the most popular sites. There are plenty spectacular destinations in and around Kyoto that are quite manageable, to even eerily empty. So, a prudent strategy would be to visit the popular sites in the wee hours, and plan out for the lesser trodden places through the day.
But it's not just the day, some of Kyoto's most spectacular autumn sites also have special illuminations that last a week or two during peak autumn.
Finally, remember to research the place you're visiting beforehand. Some have special timings for autumn, some might require advance reservations, and most of them will only accept cash. Speaking of, it can get expensive as each temple costs an average of 1,000 yen (USD 6) so be sure to budget for that.
After Kyoto, I headed to Osaka, and stayed there till early December, flying out of Kansai Airport. The earliest peaking destination is Koyasan, in early-to-mid-November. However, I skipped it this time as I was elsewhere during that time. I had been there in an earlier trip, and it's absolutely essential, autumn aside. My favourite place in Osaka prefecture was Minoh Park, less than an hour from Osaka. It's an easy hour-long hike but the entire way is draped in maple, with the crescendo being a waterfall.
I used public transport and bikeshares for getting around. Trains, buses, metros are everywhere in Kansai, with the sole exception of Kyoto city itself. Partially, while Kyoto has an extensive public transport network, it does have gaps with a limited metro network given its heritage status. Fortunately, bikeshares are available everywhere, and were a great way to cover the last mile.
As always, AMA!
As a bonus, so why are Japan's seasons so extreme? This is largely due to its unique geography. The archipelago isn't too far north - roughly being on the same latitude as Italy or Southern California, so it does get hot in the summer. On the other hand, Japan also has the snowiest places on earth. This is due to the unique quirk of being sandwiched between the humid Pacific and the frigid Siberian winds, in an archipelago that's 75% mountainous. As a result, seasons in Japan are more extreme than anywhere else on the planet, and is a significant part of its people and culture.