The empty interior of San Francisco's Pier 23 as seen from the main entrance along The Embarcadero.

Houses cling to the side of San Francisco's Telegraph Hill.

San Francisco's 210-foot-tall Coit Tower rises above the surrounding trees atop Telegraph Hill.

Detail of an American flag spotted at San Francisco's Pier 33, the embarkation point for cruises to Alcatraz Island.

A lost pair of eyeglasses, found on a sidewalk along San Francisco's Embarcadero near Pier 35.

Detail of a shipping container—an element of Tim Hawkinson's Over the Water—at San Francisco's Exploratorium.

A few of the roughly 400 skateboards that cover San Francisco's Exploratorium's "skateboard science trailer parklet" resemble the colorful teeth of an imagined monster.

One of the towers of the San Francisco-Oakland Bay Bridge rises above San Francisco Bay.

Architectural detail of San Francisco's landmark Columbus Tower, built in 1907 and now home to Francis Ford Coppola's American Zoetrope studio.

San Francisco’s 210-foot-tall Coit Tower rises above the surrounding morning sun-lit Telegraph Hill neighborhood.