Now, this one really is a no-brainer. The one Discworld subseries I'd like to spend some time in is the Witches -- simply because any place that includes (and listens to the opinions of) Granny Weatherwax, Nanny Ogg and Magrat Garlick just has to be worth looking into. And I guess being ruled by a Duke who has had his moral frame of reference and his sense of decency shaped by being the former ruler's fool (and butt of his jokes) can't exactly hurt, either ...
(Task: If you could spend time in the world of one of the Discworld sub-series (or one of the standalone Discworld novels), which one would you pick – and why?)