Roxanne Webber published a cool answer to this question on Chow today. Turns out that the “dive” in “dive bar” comes from where the entrance to the bar was located. When kitchens turned from wood fire to gas or coal the huge kitchens with their massive wood fired ovens were “downsized” creating large spaces under existing restaurants. A classic expample of this would be The Tombs in the Georgetowne section of DC (pictured above).

 Thanks to Roxanne and Chow for the interesting questions andhunted up the OED definition below.

“According to the Oxford English Dictionary, the colloquial use of the word dive to describe a “drinking den” or “other disreputable place of resort” comes from the fact that these types of establishments were originally housed in cellars or basements, into which “frequenters may ‘dive’ without observation.”

The OED says the first documented use of the phrase appeared in the New York Herald in July 1871: “One of the gayly decorated dives where young ladies … dispense refreshments to thirsty souls.” It appears again in 1882, then in an 1883 edition of Harper’s Magazine (“opium-smoking dives”). It is directly used in reference to a tavern in 1886: “A grand entrance takes the place of the tavern, which is relegated to down below, and is called a ‘dive.’””