I've always been far too lazy and self-critical to actually try to write fiction longer than, say, 5 sentences, and I'm at peace with that - I'm not much of a frustrated novelist DM. Nonetheless I do get ideas for novels from time to time. (Don't worry: this isn't a jump-the-shark post where I start posting my fiction - none of these ideas ever comes remotely close to fruition.)
When I was a teenager I had this idea for a story in which a group of explorers were travelling up a river of infinite length. I never thought about it in much more depth than that. I just liked the quixotic, "because fuck you, that's why" nature of exploring something which by definition could never be fully explored.
It makes me want to resurrect the idea, especially since I think wilderness exploration is sort of in the blogging zeitgeist at the moment (at least in the circles I frequent), and the tools for random wilderness creation are growing in sophistication and usefulness. (See e.g. Welsh Piper's stuff from a few years back, and Talysman's last minute hexcrawl.)
A randomly generated, forever-flowing river which never reaches the sea. With new sections added as and when the players explore beyond the border of the current set of hexes. Banks lined with strange civilizations and outlandish monsters. Horrible rumours about what lies downstream. Careful management of resources - gifts/bribes for the natives, food, messenger pigeons to send back home. And the prospect of ultimately giving up on the quest when Eden is found?