These secret doors with shelves attached conceal the most valuable vintages of wine in this custom wine cellar featured on Houzz.

Here's a DIY project from Saving4Six showing exactly how to add some concealed drawers under the basement stairs. They use old drawers from a dresser tand basic supplies to add unexpected storage to an unused space.

This DIY project featured on Design Sponge shows how to make a secret storage box that sits on a bookshelf and conceals it's contents behind a painting.

This bed frame from IKEA allows the mattress to pivot up and reveal a secret storage area underneath. It makes good use of wasted space, but this concept could be used to custom build a much stronger secure area below ...

This secret compartment looks like it may have had sinister intentions. It's a custom guitar with a hidden gun compartment made in Italy between 1930 and 1940.

These Function Tiles by Droog conceal compartments, dispensers and secret drawers.

This unfinished bookcase door was featured on TheChive.com in an article on secret hideaways. Not much information is given, but you cane see the classic swing-out style. The vertical trim on the right is stationary on the wall, and the ...

Spy Emporium offers several pieces of furniture with secret compartments, like this dresser with an opening base.

While not completely secret, the storage compartment in this AUTOSEAL® Kangaroo water bottle from Contigo is very useful. It's big enough to hold cash, keys and cards when you're traveling light, like at the gym, pool or beach.

This handmade hat by Knotty Strings on Etsy comes with a secret stash pocket in each ear, accessible from the inside of the hat.