This Italian band really made an excellent album back in 1972 called "Ys" and this is its opening suite. Arcane and complex, including many different rythms, tempos and moods, this 15 minutes composition features all the strong points of this concept album, based on a SF plot and vaguely inspired by Celtic legends. The sung melodies are never easy and seldom are on the verge of recitative singing, while the intricate interplays emphasize all the musicians' skills and especially the spectacular sound of Gianni Leone's multiple keyboards.
With this album BDB fully embraced progressive rock.
You'll certainly appreciate the choral arrangements, rather on the classical and experimental side, I'd say. The central instrumental passage also includes a wild guitar solo by Lino Ajello and the passage from this section to the next sung theme is one of my favourite moments of the track. In conclusion, this isn't at all a mellow Italian prog song and you'd better prepare your ears to a challenging listening.