Trying to understand native speakers. I live in Spain and still have a problem at times understanding the speed at which people speak!

Learning to hear the words. I can read and write, but listening is horrible. I have to have subtitles on when I watch Spanish shows. Oh, and let's not forget all the past tense and subjuctive.

Aside from ser/estar it's all the little idiomatic things, where particles, prepositions are not what you think they should be (because of what you use in your own language, which, of course, is not a problem of Spanish, per se, but applies to other languages as well). And of course idiomatic phrases.

Learning the endless verbs😅

The accent is difficult!