As a post-JET option, please consider Peace Boat! If you've lived in Japan for any amount of time and been to an izakaya in a major city, you must have seen posters about going around the world for 100man yen or similar. Those are put up by volunteers for a Japan-based NGO/NPO called Peace Boat, which is an organization that coordinates round-the-world voyages on a cruise ship about three times per year. The ships can carry about ~900 participants and there is a variety of programming on board and at ports of call that go beyond tourism into peace-building, international cooperation, and global citizenship.
Peace Boat recruits for volunteer English/Spanish teachers and Japanese/English & Japanese/Spanish interpreters for each voyage. There's more information here:
Peace Boat - Volunteer onboard or on land
(Note: US nationals can't apply for positions on voyages that stop at Cuba or Hawaii.)
And their main English page is here:
Peace Boat - Home
(You can check upcoming voyage dates and routes!)
After completing my contract as a CIR, I worked in Tokyo for a bit and went on Peace Boat's 78th and 80th voyages as an interpreter. It's a really great experience and you get to see a lot. It is a volunteer position (no pay, but your fare, room/board, onboard meals are covered) but I think you get a lot out of it.
For teachers, the application requirement is typically 2 years of teaching experience.
For interpreters, there is no requirement, but there is a written and verbal test if you pass the initial screening.