Why would you want to visit a city sewage treatment facility, even to find a geocache? Because if the city is Cannon Beach, it's the most beautiful such facility on earth.
The City of Cannon Beach Wastewater Treatment Facilities have more in common with a nature park than with sewage treatment. If it weren't for the fence, there are no signs at all to give away the true function of the area. It even smells just like a Northwest forest.
To reach the cache, find Spruce and 2nd in "downtown" Cannon Beach, then continue east on 2nd past the Visitor Center. Good parking is at: N 45 53.885 W 123 57.456.
There is a very easy and pleasant woodland walk of about 700 feet from the parking area. GPS reception is compromised in the trees, but the hint should get you right to it.