Really, it's whatever you're personally interested in, it should be something you actually enjoy so that you're engaged in it and honestly have something in common with the people you meet there.
Could be anything from joining a sports team, to getting more involved in politics, to taking some night classes, getting involved in a charity or church outreach or service organization, join some sort of club, take up rock climbing, or sailing, learn a language, play cards, start some sort of handiwork project like building some cabinets or tables, take up birdwatching, or photography, or music lessons, start a side business, or start brewing your own beer. Just think about what your interests are, and find ways to be active doing those things.
I would say if you are 6 months out of a divorce don't make it about meeting women, make it about meeting people, and if some of them happen to be women, that's great. Once you figure out ways of being active, you can start figuring out ways of meeting women. One step at a time, just try and enjoy your life for awhile.