California's own medieval Italian castle, authentic down to the 300-year-old iron maiden in the dungeon.

Sitting atop San Francisco's tallest hill, a cross honors the victims of the Armenian genocide.

Chevron maintains one “Standard” brand station per state so it doesn’t lose the trademark.

This print shop boasts one of the largest pinball arcades in San Francisco.

Forgotten and then destroyed by fire, this was once one of the largest saltwater swimming pools in the world.

Radioactivity still cause for concern at this urban explorer's paradise.

Alleyway plaque commemorating the death of a fictional character in The Maltese Falcon, not far from the author's home.

A speck of nature and art in one of San Francisco’s most notorious neighborhoods.

The grand, column-fronted, sculpture-adorned home of the ambitious digital library.

Adolph Sutro's little-known, geographically inaccurate, deprecated monument.

A promotional sun clock on the site of San Francisco's great raceway.

The restored and active Victorian-era final resting place of San Francisco.

An overlooked and unassuming engineering marvel.

San Franciscans leave gifts and messages for the magical beings that live behind the tiny, mysterious door installed on a tree in Golden Gate Park.

A hidden subterranean installation offers a view of the sky.

The randomness of this wall of lava lamps helps encrypt up to 10 percent of the internet.

A 300-ship graveyard, with a few still visible at low tide.

A modern mechanical planetary system, part of a 10,000 year clock.

Visible below the waves are memorials to the city's Gold Rush dead.

Tiki luxury on Nob Hill.

A walk-in working camera obscura produces 360-degree live images of the San Francisco coast.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

Get lost in this haunting fairytale art walk through a man-made eucalyptus grove.

A winding path built in secret on the edge of the continent.