The most haunting music you ever heard?

What about Fantasia on a Theme of Thomas Tallis?

FWIW I concur with the Acoustic "Under the Milky Way" I have it,its lovely.

Check out the Bax Quintet for Harp and Strings,Elegiac Trio for Harp and Violin Fantasy Sonata for Harp and Viola and Sonata for Flute and Harp by Mobius on a Naxos CD .

Anything by Genesis after Hackett and Gabriel departed, and anything after Waters 'Mr Floyd' left Pink Floyd. Still haunts me after all these years.

Leonard Cohen's "Hallelujah" by J. J. Cale or Jeff Buckley or the original 15 verse composition by Cohen himself which I heard hom perform once.

Emerson String Quartet plays Bela Bartok works on me.

Two songs on the John Hartford tribute album, done just before his death, are definitely haunting. Gillian Welch's version of "Tall Buildings" and John Cowan's version of Merle Travis's "Dark as a Dungeon".