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

A 140-year-old castle with underground caves hidden in San Francisco.

A large instrument played by the wind.

A working model of the entire San Francisco Bay and much of the Sacramento River Delta, complete with regular tides that change every 14 minutes.

Location of the most powerful laser in the world, and the potential birthplace of tiny stars.

The longest burning light bulb in the world.

Noble beasts perhaps, but not the Emperor's dogs.

An art supply shop holds the secrets of this quiet neighborhood's raucous Barbary Coast past.

With the touch of a button, you can read a randomly selected short story.

One of the oldest producers of hand-folded fortune cookies still uses its original secret recipe.

The oldest dim sum restaurant in the United States is a nostalgic jewel.

The first AIDS memorial chapel in San Francisco and one of only a few in the U.S.

Tiki luxury on Nob Hill.

America's oldest Italian restaurant is a San Francisco institution.

A classic advertising icon immortalized in regal bronze.

A mysterious painting of the self-declared Emperor of the United States watches over a local hof-brau.

San Francisco's oldest operating hotel, with a Victorian atmosphere and a "haunted" fourth floor.

The stones that traveled from Spain to eventually become a holy place for San Francisco's nature worshippers.

The remains of a 12th-century chapter house in Golden Gate Park.

Olfactory delights in San Francisco's Botanical Gardens.

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.

The one-time watch house for incoming ships at the Golden Gate now stands abandoned and hidden in trees.

A free, public museum dedicated to the fascinating science of sight.

This residential door allows San Francisco muggles a glimpse at the wizarding world.