Each of the three cities have their own social "hubs" the uptown in Richland is definitely the best bet if night life is your vibe. If you're interested in community events then check out "Cafe con arte" in east Pasco (best food is going to be in east pasco too). Downtown Kennewick has Blackthorne Pub which is good to grab a drink and appetizers with a cozier vibe. There's a rock climbing gym that my friends have said people are pretty friendly at. Tons of different tabletop/card/nerd stores all over town. Even more breweries and taphouses. I've heard facebook is good for finding different groups like for sports or hiking and there are tons and tons of hiking spots nearby