I remember Harry condensing cloud and using them as a way to move around the castle. At one point when he’s experimenting with his magic he blasts a hole in the dungeon wall. Pretty sure I read it on Archive of Our Own. He starts manipulating water at first then escalates onto other things. I’m fairly sure it was a pretty long (novel length) and well written fic but somehow I don’t really remember anything about the actual plot other than him managing to shock everyone with his new discoveries of magic. There is either no relationship or it’s slash but I think the story mainly focuses on his magic and not romance. I’m pretty sure he was in Gryffindor, and I can’t really remember any of his other experiments or discoveries except maybe at one point he managed to turn wood into gold?