I chose to retire in Athens GA in part because there is an active Osher Lifelong Learning Institute here. Olli collaborations between the community and colleges promote educational activities among older adults. In some places adults sign up for regular University classes. In Athens, the structure is more informal and classes, led by retirees and faculty, range from single sessions to weekly meetings in rooms provided by UGA.
I register for courses twice a year, in August and January and I struggle to restrain myself from signing up for too many. My favorite so far is Great Books Conversations ( a discussion of excerpts of literature that meets for 1 1/2 hours every two weeks). I also chose classes in areas I never studied before. These include The Geology of Southern Appalachia, Plays of August Wilson, Beginning Astronomy, Screwball Comedy, The Rite of Spring at 100, Improving your Photography, The Chemistry of Fireflies, etc. Each course costs about $15 per 75 minute session with a discount for classes with multiple meetings. So far I enjoy them immensely and I will continue to challenge myself with a wide assortment of courses till my memory fails me.