Horticultural, Historical,...how about joining the Hysterical Society? They are popping up in more and more communities.
Several leaders of groups in the Chicago area say laughter helps with pain management by increasing endorphins, and relieving stress.
"If you laugh on a regular basis, your body actually becomes inhospitable to negativity."
One newcomer admitted that he was always an amateur laugher and he joined to "take my game up a notch."
One warm up exercise is trying a variety of laughs such as while rowing a boat.
Quote Garden has some excellent quotes around the theme of laughter including:
~I am thankful for laughter, except when milk comes out of my nose. ~Woody Allen
~At the height of laughter, the universe is flung into a kaleidoscope of new possibilities. ~Jean Houston