Thank Jupiter for the phrase sui generis, or I'd never be able to succinctly describe Hav, Jan Morris's genre-bending fictional travel memoir. Yeah: it's not quite a novel--no characters nor plot arcs on which to hang one's hat--it's an account of a visit (two visits, actually, of which more later) to the eponymous city-state, which never existed, but is entirely plausible.
Were Hav located anywhere but Morris's imagination, it would lie somewhere in the nebulous area where Europe, the Middle East, and Asia collide, as Greek as it is Arab, as Russian as it is Turkish, with the aftermath of colonial millennia adding British, Chinese, and French to the mix. And of course, there are the Kretevs: cave-dwellers, friends to bears, and cultivators of that rarest of fruits, the snow raspberry.
(Hav also clearly borders the dual cities of Beszel and Ul Qoma from China Mieville's mindbending murder mystery The City and the City--and indeed his note acknowledges a deep debt to Morris.)
I'll admit it took me roughly half of Hav's 300 pages to start enjoying myself--as it turns out, I don't find travel memoir that interesting, even when it's technically speculative fiction. But the skill of the world-building, Morris's insertion of real history and historical figures into the story of Hav, and the wealth of charming detail (the Hav mongoose! the urchin soup! the trumpet tune that wakes the city every morning) won me over. There are two parts collected here; first, her original 1985 novel, Last Letters from Hav, and then Hav of the Myrmidons, a follow-up novella written in 2005, bringing the tale up to then. Both serve neatly (but not heavy-handedly) as allegories of their eras on the world stage, the late twentieth-century's discomfort with and glorification of the past, the twenty-first's twin demons of fundamentalism and money, as Morris returns to a Hav made unrecognizable by a Cathar theocracy and Chinese cash.
The latter is more straight dystopia territory, and hence I liked it better (OK, except for the too-precious last paragraph). This is, in fact, a book I'd recommend first to sf/f readers, partly because they've more patience with alternate histories and invented societies. Its appeal is far broader, though--rather like Hav itself.