This game is one of the must-plays of the Playstation. Everything here is top-notch: the music, the story, the huge castle to explore and the many bizarre monsters filling it. It's (not surprisingly) ranked on many 'best games ever' lists.
You can find the soundtrack here: KHInsider.com.
This OST has many great track, with lots of diversity between them.
There's a lot of harpsichord / organ / piano compositions, which feel perfect for roaming an old, baroque magical castle.
The soundtrack has a cool mix of genres, where classical compositions are mixed with slow drumbeats..there's a lot of surprising twists in the music.
Checking out the whole soundtrack and playing the game are highly recommended.