For an afternoon downtown, I’d book luggage storage near Westlake station or Pike Place Market to avoid an extra trip to the airport. You can pick up your backpack afterward and take the light rail toward Sea-Tac.

[Bounce](https://bounce.com/luggage-storage/seattle) has staffed storage locations in participating shops and hotels around Pike Place, downtown, and King Street Station. Many currently advertise rates from $3.95 per bag per day, though the total depends on the location, bag size, and fees. Book online, make sure the booking covers a large backpack, and check that the shop will be open when you’re ready to collect it.

I couldn’t find public luggage lockers at Link stations. The lockers Sound Transit advertises are for [bicycle storage](https://www.soundtransit.org/ride-with-us/know-before-you-go/bikes-scooters/parking-storing-your-bike).

At Sea-Tac, [Smarte Carte baggage storage](https://www.portseattle.org/services-amenities/baggage-services) is between baggage carousels 9 and 10. It’s open from 7 a.m. to 10 p.m., with breaks from 11:30 a.m. to noon and 6 to 6:30 p.m. You don’t need a reservation.