Seattle guy here. Off the top of my head, here are the places I can think of with open showers.
Downtown Seattle YMCA: Yes, they have open showers, and no, I do not recommend going. This used to be the cruisest place in the world; I loved this gym and would go all the time and always get action. Well, I guess word got around cuz they instituted a ban on nudity in the Sauna, steam, and whirlpool, so that’s officially ruined. I wrote an angry letter but nobody’s listening, we gotta be sensitive to those stick up ass straight people who aren’t going to use the shower area anyway cuz they’re so terrified of nudity. So don’t go to this gym and support them.
Bellingham YMCA: Thankfully, this is the last YMCA in my area I can find that still has the classic set up and still lets everyone walk around naked. Naked sauna, naked steam room, naked old style showers. It’s a small town so while it can be cruisy, it can also be incredibly quiet and boring depending on the day. On my last visit, I stayed a long time and had a delightful time with a hot black guy, a hot Hawaiian, and saving the best for last, a beautiful Asian. Day pass is 12 dollars and I do recommend it.
Ashland Family YMCA in Ashland, Oregon: Now, I want to make it clear I haven’t been to this Y since 2012, but I went all the time for four years. Perhaps the layout has changed since then but I kinda doubt it cuz I believe the facility was built in 2005 so it would be pretty early to do a remodel. Anyway, when I went there, it had open showers and a sauna that everyone used naked. One caveat, however, is that Ashland is a very hippie place, so while the penises flopped left and right as far as the eye could see, it wasn’t necessarily cruisy and I didn’t hook up very often; it was more just happy Nudist types who don’t care about being naked.
Palace Spa in Federal Way, Washington: A day spa that costs 25 bucks to enter and has a men’s area and a women’s area. Nudity is actually required there so there’s no excuse for being shy. Open showers, three whirlpools, sauna, steam. Can definitely be cruisy but discretion is a must; awhile back I got caught getting a hand job and got thrown out. While it’s been like three years now and I’m fairly certain nobody there would recognize me, I haven’t gotten up the courage to go again.
Q Spa and Sauna in Lynwood, Washington: Same as above, a day spa that can be cruisy. Naked showers, whirlpools, sauna and steam.