If and when we get a place with a backyard, I will resurrect a hobby/obsession that I had a few years back, that's been on the back burner.
Pretty much from out of nowhere in 2004, I became hardcore obsessed with Bonsai trees. I didn't have a lot of space, so my practical capabilities were limited, and I had ,um, varying degrees of success in keeping them alive.
But what obsessed me was the theory of it all. From time to time I would shell out for a new book, and I would pore over it, reading every last word and footnote about it, learning as much as I could about the different styles, and memorising all the different species of trees.
Then we moved to a place without a yard or balcony, and my enthusiasm quickly dried up. But it's just in hibernation, and when/if we get a backyard, the first thing I'll do is pull all my books out again.