Of all the languages I really want to go deep with and learn my #1 has been #CommonLisp for like 5+ years now. I know it's not the most relevant (#Rust) or hip (#Haskell) but it's just such a fundamental. And I had so much fun writing it when I was learning it. Need a project idea to use as an excuse to learn it.
@jsatk It's getting a little older now, but I found the book "Practical Common Lisp" by Peter Seibel was excellent for learning Common Lisp. It includes some project ideas that should be helpful.
@danielwaechter I own that one. I just gotta actually read it which is a huge time commitment