The Charles gate highway overpass project is an urban hybrid adaptive reuse project dealing with underused infrastructures. The space beneath the highway overpass is reactivated through this intervention. I discovered the site’s connection with water body pollution issue of Charles River, Boston. And with the existing conditions, developed a self sufficient program that harvests the water purification process and turn the site into a community friendly spa, or according to the way it works, an ONSEN. The Charles River Onsen.