Going to Crystal Mountain, taking the gondola up and having a bite to eat while super close to Mt Rainier is an unforgettable experience: https://www.crystalmountainresort.com/
For those that do not want to hike, driving to Paradise or Sunrise, inside Rainier National Park, would allow you to enjoy the views without the need for hiking. Those areas require a timed-entry reservation for entry between 7am-3pm (outside of those times, a timed-entry reservation is not required). New reservations are made available at 7pm for next-day entry. More information at https://www.nps.gov/mora/planyourvisit/timed-entry-reservations.htm
For a longer getaway, the Olympic Peninsula has stunning beaches. An idea would be to stay in Forks to visit some of the beaches, or stay in Neah Bay to visit Cape Flattery, the northwesternmost point of the contiguous US.
Leavenworth, the German town close by, is a fun day trip.
Diablo Lake, in the North Cascades, is absolutely stunning.
From Seattle, the ferry to Bainbridge island is very easy to take (with or without a car, reservations not required).
For a longer day trip or weekend adventure, it's also super fun to take the ferry to go to Orcas or San Juan Island. You need a reservation to take this ferry with a car.
Drive through Deception Pass to go to Whidbey Island. The town of Langley is a fun spot to stop.
Drive to Artist Point, close to Mount Baker. Insanely beautiful views even for those who don’t want to hike.
Bellingham is a cute little town by the ocean which makes a good stop for those going close to Mt. Baker.