I can't think of anything to obscure. Except maybe Chatterton by Peter Ackroyd, or A fine and Private Place by Peter S Beagle.
Tim's comment just remimded me of a book I read years ago by Margurite Yourcenar called The Memoirs of Hadrian, a truly great example of historical fiction. A writer who I suspect is worthy of more attention.
On the subject of obscure books I wish book shops would stock greater variety, everything seems so mainstream, it seems as if a book is not subject to a current marketing campaing you won't find it in your average small book shop.
Actually, Sharon, "The Memoirs of Hadrian" is very similar to "The Abyss" in style. Personally, I think that "The Abyss" is slightly better, but maybe because I read it first. Her "Coup de Grace" is also abolutely brilliant, and totally different - it has the most devastating ending I have ever read. And, if you liked "Hadrian", you may well also like Clive Ashman's "Mosaic" about a 4th century British mosaic going missing immediately after World War Two (true story), and the fictional history of the guy whose mosaic it was - a powerful dissection of the uncertainty of the time from both within and without the late Roman Empire.
And, yes, I loved "Chatterton" too - in fact, I am a big Peter Ackroyd fan. "Hawksmoor" is also brilliant. His "Oscar Wilde" book has one of my favourite literary quotes - "She [Wilde' wife] is very quiet in company, but she is not at all quiet about them when they have gone home". Not an exact quote, but you probably get the drift.