We're all familiar with the quote: "You can't judge a book by its cover." The same rule applies to restaurants. Even though some restaurants may not look like much from their exterior, they may serve the most delicious food you'll ever eat. And some of these restaurants may not look like restaurants at all. There are several 'hole in the wall' restaurants located throughout Alabama, and the 15 restaurants listed below are some of the very best.

1. Big Spring Cafe - Huntsville, AL

Big Spring Cafe opened in 1928, making it Huntsville's oldest operating cafe. It's also known as the "Home of the Greasy Burger."

Pictured: Cheeseburger & Fries

2. Down South BBQ - Foley, AL

Down South BBQ serves some of the best barbecue on the Gulf Coast. A few of the delicious food choices this BBQ joint offers includes BBQ plates, delicious side dishes and their famous cornbread sandwiches.

Pictured: Cornbread Sandwich

3. Mrs. B's Home Cooking - Montgomery, AL

Mrs. B's Home Cooking features down-home, Southern cooking that's served cafeteria style. Customers simply enter the food line, grab a tray and load up on delicious meats and vegetables. Everything is delicious at this popular Southern-style restaurant.

Pictured: Vegetable Plate

4. Po Boy Factory - Huntsville, AL

Po Boy Factory is a Cajun and New Orleans seafood restaurant that's well known for its delicious made-from-scratch dishes. Most of the dishes from their menu costs less than $10, which include popular food items such as po boys, shrimp, jambalaya and oysters.

Pictured: Crawfish Po Boy

5. La Placita Mexican Grill - Madison, AL

La Placita Mexican Grill is one of the best Mexican restaurants in the Madison area. The portions are huge, prices are great, and the service can't be beat. What more could you ask for?

Pictured: El Luchador

6. Flip Flop Deli Shop - Gulf Shores, AL

Flip Flop Deli Shop is a great place to grab a bite to eat during lunch. Don't forget to get yourself some of their delicious ice cream before you leave.

Pictured: The Danielle - Pizza Sub

7. The Choice Restaurant - Gadsden, AL

The Choice Restaurant, located in downtown Gadsden, is a popular spot for breakfast and lunch. Everything is homemade and the prices are very reasonable. You won't leave disappointed.

Pictured: Breakfast Plate

8. Greenbrier Restaurant - Madison, AL

Greenbrier Restaurant is a local favorite that specializes in catfish, barbecue and seafood. Due to the diversity of Greenbrier's menu, there's something available for everyone.

Pictured: Ribs & Fish Combo Plate

9. Kitchen on George - Mobile, AL

Kitchen on George is one of Mobile's finest restaurants. It's located within the Oakleigh Garden Historic District and its incredible dishes are created from locally sourced ingredients.

Pictured: Tempura Fried Okra & Roasted Tomato Soup

10. The Garage Cafe - Birmingham, AL

The Garage Cafe not only features an amazing courtyard, but it's also home to one of the most amazing bars in Birmingham. When it comes to food, their specialty sandwiches are incredible!

Pictured: BLT

11. Archibald's BBQ - Northport, AL

Archibald's BBQ is best known for their amazing ribs. According to "USA Today" and "Good Morning America," they have some of the best ribs in America.

Pictured: Small Mix Plate

12. Taqueria El Cazador - Huntsville, AL

Taqueria El Cazador is a Mexican restaurant that's located inside of a bus. What makes this restaurant unique is the fact that guests can actually eat inside the bus, even though there's limited seating. For authentic Mexican cuisine, you should definitely check this restaurant out. They're best known for their tacos, but all of the menu items are delicious.

Pictured: 4 Taco Plate

13. Sammy's Sandwich Shop - Birmingham, AL

This family owned and operated sandwich shop is known for serving the best burger in town. It's also a popular lunch spot among the locals.

Pictured: Cheeseburger

14. Holy Smokes BBQ - Scottsboro, AL

Holy Smokes BBQ is possibly the best BBQ joint in Scottsboro. Their fall-off-the-bone ribs are incredible, and their stuffed baked potatoes are a definite must try.

Pictured: Stuffed Baked Potato

15. Tip Top Grill - Hoover, AL

In addition to offering their guests a spectacular view, Tip Top Grill also offers delicious burgers and hot dogs. At one time, this unique restaurant was a gas station.

Pictured: Little Cheeseburger & Big Cheeseburger with Fries

What other restaurants would you add to this list?