Bois de Santal is one of the 25 or so fragrances in the Keiko Mecheri line. It has notes of Indian sandalwood, white osmanthus, golden ambergris, tonka bean, and Moroccan ambrette.
Bois de Santal is one of my favorites from this house. The name strikes me as an unfortunate choice — it is not likely to impress someone looking for a straight sandalwood fragrance — but it is well worth trying if you can get past that. It does start with a nice burst of wood notes, but that fades rapidly, leaving behind a transparent floral over a pale musky-woods base. There is a touch of amber, a muted whisper of tonka bean, and possibly some cedar.
The osmanthus here is nothing like the bright, tropical osmanthus of the Keiko Mecheri Osmanthus perfume (see link above): it is very soft, a bit warm, and not particularly fruity or sweet. It is an understated kind of fragrance, with something very calming about it, and while it stays close to the skin, it has very good lasting power. I find that it wears best in temperate weather: it is not strong enough to stand up to deep winter, but is probably a bit much for the very hottest days of summer.
A 75 ml bottle of Eau de Parfum is $80. I do wish that Keiko Mecheri would make smaller bottles. I keep hearing rumors that the line is to be repackaged again, so perhaps that is in the cards. For buying information, see the listing for Keiko Mecheri under Perfume Houses.