From 31 July there'll be a labyrinth of books in the Clore Ballroom. It's called aMAZEme and is part of the London 2012 Festival. People can wander round it and see spoken word performances until 26 August (for free), but first the thing has to be built. aMAZEme have put out an appeal for volunteers on Craigslist – they need people 26-30 July to take 250,000 books and build walls up to 3m high. They'll give you food and drink for helping out (they also need a hand taking it all down again on 27 August). Drop firstname.lastname@example.org a line.
The Southbank Centre is also looking for volunteers to help build a map of the world out of Lego bricks, on the Riverside Terrace. Although technically you wouldn't be playing with the Lego yourself, we're sure there'll be opportunities. Officially they need people to help visitors complete their own piece of the map, and generally be bright and friendly and give the UK's only certified Lego professional, Duncan Titmarsh, the space to take care of the project. The dates are 23 July-10 August with training this Friday; the application document says you need to be able to do five shifts and it looks like those shifts would be full days.