In the first area on the summit of Olympus you get this nice effect of rain droplets running down your screen, unfortunately it only appears in this one area. I have some suggestions for more areas where this effect can occur.
-(The Summit) In the Hermes trading chamber before the final boss.
-(Ephyra when it rains) The hub, Medea's encounter and the Charon trading chamber.
-(Erebus when it rains) the fountain chambers, The Charon chambers and Arachne's chamber.
- Potentially also The Crossroads when it rains