Pusan?
How about Shiretoko in Hokkaido? Stupendous, breath-taking natural scenery and happily fairly free of tourists. A rugged sea coast and lots of wildlife. You fly from Haneda to Memanbetsu Airport, about 1.3 hours, and it's an hour or so away.
Or Shirakami Sanchi in Aomori - glorious mountain scenery - like a painting - and perfect for autumn. (If you have an international driver's license you can rent a car in Japan.)
I've been to both and they are out of this world.
For something very different, try a few days on Ishigaki, or maybe Ogasawara.
Ishigaki is an island in Okinawa Prefecture and Ogasawara is also a groups of islands. Ishigaki is tropical and Ogasawara semi tropical. You fly from Naha to Ishigaki, and for Ogasawara (which was once American territory but for some reason was given back to Japan) you take an overnight steamer from Tokyo. Very exotic places!
BTW, the Tokyo Tourist Office on the basement floor of the Tokyo Metropolitan Government building in Shinjuku offers FREE walking tours of many parts of Tokyo, including some not often visited by noisy tourists. They provide them for groups of up to 5, and in English, German, Spanish, Chinese, Korean, Italian and even French. I have gone on 2 and the guides were fluent in English, gracious and extremely knowledgeable. I highly recommend these tours.
If Japan is getting old (and it can, quickly, I know), how about Pusan and the rural parts of southern South Korea?