Should I use the River of Light in this cavern?

Hint 1 of 5:

Not initially.  That is, not upon first visiting the cavern and talking with
Londie.

Hint 2 of 5:

You can certainly try the River of Light, at least to visit the Cepheid Road
and the Plain of Sand.

Hint 3 of 5:

Nothing much will happen until you have accomplished several other things
first.