How exactly do you use Roche's Bell?

[Bouchacha]

I know you press enter from the inventory to ring it, but the only response I get after solving the respective riddle and defeating the spectral knight (or whatever) is something like "rings weakly". Am I supposed to do something more specific?

[nul]

Use it on the overworld. It'll have an extra effect.

Spectral Knights are also completely unrelated to the bell.

[Bouchacha]

All it says on the overworld is "the bell is barely audible". Does the bell have any use besides the ossuary?

[nul]

It should also put a particle effect on the overworld when you use it there. Which will point you to where you need to go.
Might be a good idea to hotkey it instead of opening the inventory.