Hole in the wall

Context #1 

Sam: Last night we found this really awesome restaurant for authentic southern BBQ!
Tony: Really?  Where is it?
Sam: It's a tiny little hole in the wall right on the corner of Main St. and First.  The food is cheap and delicious!


Context #2 

Jenny: So, how was your trip to San Diego? 
Sara: It was great!  We found this little hole in the wall downtown that had the best Mexican food I've ever had.
Jenny:  Wow! That sounds good!

Meaning: In American English, the term hole in the wall is used to describe a small restaurant that is usually cheap and delicious, but sometimes a little dirty looking.  It sometimes can mean that the place is a little dirty looking but with good food or a cozy atmosphere.