London Open House Weekend is coming. Registration for volunteering is now open - more here I've done this a few times - usually selecting a smallish museum but there's a variety of heritage / architectural sites open. Means committing to a morning or afternoon somewhere, and as a steward, usually doing the basic meet / greet / front of house stuff / queue management where necessary - to give the regulars a chance to answer the more complicated questions. you can volunteer as a guide if you're a bit more knowledgeable / prepared to learn about wherever it is. you get a free copy of the printed guide book thingy, and a priority badge that (i've never tried it) gets you priority admission at venues (not the really high profile ones where they draw names out of a hat or whatever) and (in my experience) get fed tea and biccies.