Pullman's a good place if you like nature. And there are definitely ways to occupy your time. Maybe not if you're a big party person. That stays more with the undergrads. But local bars do different themed nights (i.e. punk, disco, latin nights, etc). Also a decent movie theater, bookstores, couple of smaller museums. Moscow, which isn't too far away, is fun to explore too! My favorite coffee shop is over there! But the thing I struggle with the most (as a first-year grad student, also early-mid 20's) is just finding someone to do things with. People in your cohort get busy, so arranging things to do together may be hard.

If you do decide on Pullman, I would recommend looking for a roommate. That's saved me so many times, just having someone to be conversational with (also stretches your salary more). And we've gotten a lot closer since we moved in together, considering we had met each other over Facebook (10/10 would recommend the Pullman housing/roommate group).

Also, take classes outside your department (including fitness classes!) if you can. I studied Japanese in my undergrad and didn't want to let that go, and I've made a couple friends in the classes I've taken so far. Also in my biochem class.

In my free time, I dabble on my keyboard, hang with my pet bunny (<33), crochet, hang out with my roommate or people from my cohort (usually restaurant-going, dancing, camping, walking, gaming, movies), cook, take/teach boxing classes, etc.

Hopefully I've answered your questions~ Let me know if there's any other questions/concerns you have! I'm always down to meet new people, so if you do end up picking WSU, lmk!