"The Witch of Atlas" is a fantastical, if not flowery, poem which Shelley evidently dedicated to his wife Mary with a few extra stanzas at the beginning addressing her. Now, it's admittedly not strong in its structure concerning plot, but gosh this is interesting at the very core. So a Witch lives on the mountain that Atlas lives on. She makes a hermaphrodite, neither male nor female by classical definition. Various difficult-to-follow adventures ensue. And that's all there really is to it.
So when I did know what was going on, this was a nice little poem. But for the most part, Shelley has a problem when it comes to longer works, which is that he is much too flowery and philosophical to create understandable content. Very lofty stuff, but a little too much.