This BONUS physical cache is associated with the Adventure Lab Architectural Details in LaConner. You must complete all five stages of the associated Adventure Lab to learn the location of this cache.
To complete the Adventure, you must visit 5 locations and answer a question correctly at each stop. The Adventure Journal will include a hint for each correctly answered question. Taken together, they will provide you with the final coordinates to the bonus cache.
The walk through historic LaConner is about 1/2 mile (1km) and can be completed in less than 60 minutes. Your adventure may take longer - with many shops, restaurants, bars, and galleries, there is much to see and do in historic La Conner. You may check the final coordinates here.
CONGRATS TO 2ND1OF 3 FOR FTF