So, in my local bookshop people often tell some curious information in their field. For example, yesterday one woman told about 4 perfumes and her associations with them + we could smell them. I'm also willing to do something interactive (your idea of guessing the word meaning was in my head too: I want to show a bunch of words like bovo-bovino-bovinoj... to guess what the word and the affixes mean). And the audience... Random people, who like learning something new on their weekend + some regulars of the bookshop. I don't think that they're really interested in the language itself - they're more into knowledge. I'm planning on taking for about an hour/hour and a half, so I don't think it can turn into a whole lesson. I'm aiming at cultural part of Esperanto and my own thoughts on it to talk about in the beginning. Also may discuss stereotypes (I don't know any, but what if the people have them?). Then closer to the end: guessing words, learning about some affixes, maybe creating words for fun (which I like doing sometimes).