When Rivers in the desert plays?

[Exarch_Alpha]

In which boss? I beat the 4 th pace and it´s always the same boss music, which isn´t bad but still.

[Lemiru]

7th palace is the earliest it plays if I remember correctly

[Nibbie]

I think the instrumental is the 6th, with lyrics for the 7th, something like that.

[Xelane]

It plays for the 7th palace boss theme (once instrumental and then with vocals)

And for all the secret boss fights (of which there are 3, IIRC).

[Ulqui210]

It starts playing at the 7th palace if this is your first playthrough.