If you're looking for a detox from all the large-scale, corporate-sponsored festivals we've been seeing of late, this should do the trick. Since starting life in 2006 as an 'oversized barbecue party' with a single stage, Tone River Jam has expanded into a three-stage affair that nonetheless hasn't lost its DIY ethos – and, yes, it's still free to get in. The main stage lays it on heavy with the punk (Locofrank, Garlic Boys, Four Get Me A Nots, Dustbox, etc.), but you can expect a wide variety of music elsewhere, be it taiko group Gocoo, jam bands Dachambo and Soft, or Fela Kuti devotees Jaribu Afrobeat Arkestra.
Getting there: Take the JR Joban line from Ueno or Nippori Stations to Tennodai. A shuttle bus runs from the north exit (¥100 one-way).