Instead of a specific class, I'm going to recommend a type of class: the small, reading-focused seminar. Here are some benefits I can think of just off the top of my head:

1. The small class size allows much much more interaction between students and between students and the professor. I (and many others) learn much better in a discussion setting rather than a lecture setting. Plus, there's nowhere to hide: you can't just not show up to class without anyone noticing, you can't not participate without anyone noticing, etc. This increased accountability is a good thing.

2. Doing deep reading in one particular area is hugely beneficial for learning more generally. By getting super-involved in one field, you learn that every different field of study has so many intricacies and you get a deeper appreciation for that. You also learn how to deeply research a topic, which is obviously beneficial for life.

3. Most of these reading seminars end in a long research paper. I don't know about you, but most of my long research papers previous to this were for freshman writing classes where they just spew some dumb formulaic rules at you, and I'm pretty sure if anything I came out of those being a worse writer. Not so in the small seminar. Since the focus is on the content rather than the writing style itself, you learn a lot about argumentation in that particular field, how to critically think about a specific topic, and by doing so your writing ends up being better anyway.

Pick some topic you're interested in, say history for example, and see if there are any upper-division reading seminars you can take; my best experience has been those where enrollment is capped at around 15. Many of these classes will probably have prereqs you haven't taken, but you might be able to find something. Plus you can always ask if you can have the prereqs waved.