SEATTLE — Whether it takes the form of logging detritus or the ruins of a cabin once belonging to an influential Seattle family, signs of human intervention in the wilderness can be a novel sight — and even an unsettling one. But if you feel like you’ve hiked every hike within a two-hour drive in our year of COVID-19, finding something unexpected along with your elevation gain can be a way to break up the monotony, and Washington state is home to plenty of these mystery hikes, complete with unnatural wonders.