There are plenty of resources to get a good view of the opportunities that exist. One place to start is by asking friends, family, and colleagues. Another option is to use one or more of the many tools created to help identify volunteering ideas that may deserve your consideration. For instance, Serve.gov is one such tool run by the federal government. Another website you may want to review is Volunteermatch.org.
Another approach may be to pick charities that you support and check out their volunteer opportunities. Don’t be afraid to call them since some opportunities may not be advertised.
If you do choose to volunteer during retirement, you may find that you will receive as much as you give.