It does make a difference that you're a lady, because where you must go is Olympus Spa in Lynnwood.
Olympus is a Korean style bathhouse- this means ladies only and nudity required in the pools. You may be surprised to learn that being nude around middle-aged Korean and Russian ladies is not an intimidating experience.
$35 gets you in the door and unlimited access to four pools of varying temperatures, a mugwort bath, humid and dry saunas and six relaxation rooms with different kinds of herbal infusions and some complicated Eastern heating system that apparently provides a slew of health benefits. There are places to lounge and read, places to chat with friends, a delicious restaurant and a tea room. You can stay there all day without purchasing any spa packages (many women do), but if you want to go all out get the Korean body scrub and moisturizing treatment. This is not your typical wimpy Western style exfoliation; you will actually see dead skin rolling off your body. Lots of it. Have you ever wondered why so many older Asian ladies still have flawless skin? This is why.
So, in conclusion, the Olympus Spa is where you must go.