Take online classes through Coursera, or look into local community colleges where you can take one class a year. I took a course on WWII a couple of years ago and it was great! Evening classes are your best bet (at the 200 level) for good discussion at a community college since it tends to be more of the "older" students who are taking the class because they're genuinely interested in the content as opposed to students just trying to fill up credits to earn their Associates (at least that has been my experience).

Plenty of researchers put their papers up on Academia.edu that you are free to access and read.

Continuing ed/university outreach, maybe?

My university does public "salons," aimed at alumni/the university-educated crowd once a month at a local restaurant. Involves a lecture from a prof, and then discussion. I've never been to one, but I've heard good things from people who have.

Find a topic that interests you and read everything you can find on it. Eventually you'll find some aspect that hasn't been covered yet, and that's you sorted.