If memory serves, one of the ways to penetrate Viper Manor (a nighttime sequence) is to climb the bluffs and come in the back way. I think it depends on your party. I never needed to climb them at night, unless I'm forgetting something else. There's also the scene later that night where Serge jumps off the bluffs into the water below. That may fit in somehow.
It's been too long since I've played!
