The booming tech economy means a lot of former abandoned places (like creepy hospitals in the Presidio, the Transbay Terminal, the Hunters Point Naval Shipyard, and the Fleishhacker Pool) have mostly been taken over by real estate developers (or the SF Zoo for that last one). It also means high rent and plenty of empty storefronts and countless "Retail for Lease" signs. But there are some especially haunting abandoned places in San Francisco worth a little more exploration. Some require a ferry, while others simply require some serious nerve.

1. Alcatraz (aka The Rock)

An island paradise?! It looks so inviting from across the Bay—well, maybe if you squint your eyes…

Alcatraz began housing Civil War prisoners as early as 1861. It eventually became a federal prison in 1933, but closed only 30 years later because it was so expensive to operate. Now, it’s one of the city’s most popular tourist attractions.

A haunting look inside a cell. Who slept here? Could it have been Al Capone? The Birdman? George "Machine Gun" Kelly?

2. Bayshore Roundhouse

Built in 1910, this area on the edge of Bayshore was home to a large rail yard for steam-powered freight engines, plus shops and even a hospital. Once diesel engines replaced the steam-powered ones, the roundhouse was abandoned in 1982.

A fire in 2001 destroyed much of the roundhouse, though the bones and remains have become a favorite medium for graffitists.

There are tentative plans to develop the surrounding land, while preserving the roundhouse for a railroad museum.

3. Sutro Baths

Built in 1894 by self-made millionaire Adoph Sutro, Sutro Baths was the place to kick back and have some oceanside fun filled with slides, springboards, trapezes, and a high dive.

Over time, the baths lost their luster. By 1964, developers planned to build high-rise apartments on the site (sound familiar?!), but a fire in 1966 destroyed most of the area and it was left in ruins.

Today, it’s a popular attraction and photographer’s dream (it’s a great spot for engagement photos). Make your way through the cliffside tunnel for some spine-chilling action.

4. Cosson Hall

Opened in 1969 on Treasure Island, this naval barracks contains two asterisk-shaped buildings made up of six wings and a central, circular ramp. This was home to sailors stationed on the island.

The building was decommissioned in the 1990s, and has since become a playground for spray-paint artists and urban spelunkers.

Some claim the area is haunted. We’re not going to argue.

5. Angel Island

Just like Alcatraz Island and Treasure Island, Angel Island has a strange, fascinating history. It’s been used for military purposes, as a quarantine station, and an immigrant inspection and detention facility.

The military post was decommissioned in 1947, and a Nike missile station was soon installed.

Today, many of the old buildings — the main barracks, an immigration center, and hospital — have been or are currently being restored, but there's still plenty of haunting spots to discover, like Fort McDowell, used as a port during both world wars.

Have you explored any of these historical spots? What other abandoned places in San Francisco do you find totally haunting?