Just to check you're in the right place to begin with, the Harpy beach is accessed from the druid grove, from the circular area where the ritual is being performed when you first arrive. You take the first left after coming down the stairs to that area, in front of Volo and the bear.
Then you take the left main fork (the right takes you to Alfira) and generally keep heading downhill. There are a couple of dead-ends that let you fan out along the cliffs, that you may want some of your party to do to help in combat, but the main path down to the beach should be reasonably clear.
Does that help? Or is your problem something different?
"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"
