I'm going to tell you the hardest ones I took:
Anatomy and Physiology
I took this class the summer after I finished my freshman year of college. I took it at a public state school where my extended family lives. I wanted to get one of my science requirements out of the way and this was one of the only things offered and I figured it may help prepare me for my physiological psych class that I'd have to take later on (I was a psych major). Oh this class...After the first day I called my mom and told her I didn't think I could do it 'cause it was too hard. I stuck through it and after tons of perseverance, frustration, and extra credit, I managed to pull off a B. I accepted it and was so glad I didn't have to take part 2 of this class like many of pre-med, nursing, and other science majors and majors that required the other part. Good riddance.
I'm not gonna lie though, I was proud of myself for making it through 4 weeks of that bullshit. This was even worse than the Math for Liberal Arts class I took my first semester (it's in between remedial math and college algebra basically). Ugh.
Women and Religion
This class wasn't like A&P in the sense that I didn't necessarily struggle with the material. It was the amount of work we had to do that was hard (papers and the tests were no joke). If you did not have decent writing skills, you were basically screwed on the exams. This was both one of the hardest and the best classes I ever had. I learned a lot about women in different religions and it erased some of the ignorance I had and also taught me a lot about religion in general. It was a very interesting class and for one assignment we had to visit a religion of our choice's place of worship. I chose Buddhism and really enjoyed visiting the center.
I had a few other classes I really enjoyed, but in terms of something being "hard", those are the two I had to put a lot of time and effort into. One of them I enjoyed, and one of them I hated.
What were some classes you thought were hard, either in terms of time and work, or just you struggling with the material in general like I did in A&P?