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

Golden Gate Park's historic collection of plants.

Over 315,000 preserved amphibians and reptiles in jars.

A collection of 20th-century automata, penny arcade games, and musical contraptions.

In all of the 29 years it was in operation, no prisoners ever escaped successfully... or so they claim.

A pier that used to act as a busy ferry dock is now a decaying favorite of local fisherman and urban artists.

A historic hotel in an old California railroad town with a rowdy reputation.

These old stone ruins in the Oregon wilderness were once bathrooms and are steeped in legends of murder.

No two pieces are exactly the same at Portland's hippo-themed hardware store.

The now-abandoned tunnels were built for the transcontinental railroad on the route where the first wagon train entered California.

A lawless town deep in Death Valley was famous for its riches and death rate.

This historic mini-suspension bridge was swept away once but is now here to stay.

This stoic, if derpy, giant stands as a monument to Oregon's statehood and the novelty culture of yesteryear.

This historic black and white monastery is one of Bulgaria's architectural jewels.

A spectacular Bulgarian cave resembling a devil's head with a waterfall rushing down its throat.

This ancient theater, restored in the 20th century, lives on as a venue for dramatic and musical performances.

Monasteries on rock pillars, once accessible only by frayed ropes.

A striking symbol of the Bulgarian capital.

This once-grandiose behemoth of a monument from the socialist era now sits quiet and closed up.

This cabin once belonged to one of California's original settlers.

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

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

Big gun installations, built over a massive cemetery, now abandoned & hidden in trees.

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