Marker for the Exploratorium Department of Operations’ electrical junction box shown in the concrete floor which houses a radiant heating and cooling system. (Photo by Mignon O’Young)

Marker for the Exploratorium Department of Operations’ electrical junction box shown in the concrete floor which houses a radiant heating and cooling system. (Photo by Mignon O’Young)

Marker for the Exploratorium Department of Operations’ electrical junction box shown in the concrete floor which houses a radiant heating and cooling system. (Photo by Mignon O’Young)