According to the Guinness Book of Records, the narrowest street in the world is located in Reutlingen, Germany. In reality, it's just a passageway, an exit from a rear courtyard. In the eighteenth century, this district was completely destroyed in a huge fire. To ensure that, in future, fires couldn't spread so easily from house to house, a narrow space was left between them. Measuring just 31cm in width, it quickly went into the record books as the narrowest street in the world, even though it isn't much of a street.
Previously, this record was held by the Parliament Street of Exeter, England, which in my opinion fitted better to the definition of a "street". This 50m long street which links the High Street to Waterbeer Lane and dates back to the 14th century is approximately 1.2m (45 inches) at its widest and less than 0.64m (25 inches) at its narrowest. Formerly it was called the Small Lane before being renamed in 1832.