I am looking for the title of a book that I read a while back. It was a Penguin Modern Classic 70s edition of a French novel, by someone along the same lines as Andre Gide. It was written some time after the WW1 and I remember the title being translated as something like The Lost Garden, or The Secret Garden or something similar (I am definitely NOT talking about 'The Secret garden' by Frances Hodgson Burnet).
As far as the plot goes, I seem to recall it being about a brother and sister who go on a expedition and find some sort of mansion to which they keep returning to. I can't remember too much more about it unfortunately, though I do remember that I read it at the same sort of time that I read The Immoralist and Les Enfants Terrible, and it seemed to fit in quite well with those other novels.