Japan's Tokai Shizen Hodou, or Tokai Nature Trail, is little-known despite being 50 years old.  This trail encompasses 1054 miles/1697 km, including all of it's alternate routes, but is about 600 miles/1000 km from end-to-end.   Although it can be thru-hiked in about 5 weeks, this trail is perfect for section-hiking because it is so accessible along most of it's length by public transportation.  If you truly want a deep experience of Japan, this trail is one of the best ways to access it.  Running through lower mountains at about 300m-1300m altitude (1000-4000 feet), this trail is best to hike in March-April or September-November.