I know that this is the cycling community, but… Why would someone choose to bike to Costco unless they are an employee? Are there people who do not purchase a carload of goods when they go? Cyclists are nowhere near Costco’s target demographic, so this really doesn’t seem surprising.
I introduced a “small one story structure, its walls no wider than the span of a single door” next to the farmhouse my players were investigating. They didn’t believe the owners who told them what it was for, and went to check it out for themselves, hackles up and weapons drawn.
It’s an outhouse.
Just an outhouse.