Invite Brian Carwana to come and teach a different religion every week or every month (or, if you are far away, combine several classes into a weekend of world religions). The classes are great on their own or paired with visits to houses of worship. 

Brian's overviews of the different religions are exceptionally popular and often create growing audience sizes via word of mouth. These series have been particularly favoured by Later Life Learning groups, University Women's groups, professional organizations, and religious congregations.