I do NY Times crosswords. quite challenging as an ESL, but very satisfying. so far I've only been able to solve Monday or Tuesday ones, and I still use the "check puzzle" helper to see how many words I got wrong when I'm stuck, but I don't have to look up stuff online anymore!
there's another layer of difficulty when you're not from the US, as it often requires you to know stuff from US history and culture that you don't learn and know about abroad. like tHE FUCK KIND OF A THREE LETTER ORG DID NIXON CREATE, WATERGATE IS LONGER THAN THREE LETTERS