if you don’t need credits, mit ocw is probably the most rigorous and also free. i’ll give you more suggestions if you watch anime. since you swim and you’re a girl, there’s a swimming anime with a lot of half naked guys (recommendation based on a very general stereotype (parentheses included so people won’t get super offended and start calling me super sexist and anti-lgbtq or stuff (i’m scared of very sensitive people (actually just watch the anime i’m in))))