Elda and Ray Behm built and tended an awesome garden for over 30 years until the Port of Seattle decided they needed the property for a new runway at SeaTac Airport. Members of the community got together and helped Elda move most of her plants to this site, which is now known as The Highline Botanical Garden featuring Elda Behm's Paradise Garden.
The cache is located outside of the garden, but if you can visit when the garden is open, I am sure you will enjoy your visit. No bushwhacking is required, because the stash is only a few steps off of a trail.
This place is about a 2.5 mile walk from the SeaTac terminal, so it might be worth a visit during a long flight layover.
Parking and garden entrance are located here:
N47 28.770 W122 18.236