Most of the photos on this site were extracted from reference images (high-resolution tiffs, 20 to 200 megabytes in size) from the Library of Congress research archive. (To query the database click here.) Many were digitized by LOC contractors using a Sinar studio back. They are adjusted by your webmaster for contrast and color in Photoshop before being downsized and turned into the jpegs you see here.
The year is 1924 and the city is Washington, D.C. What's going on here? Your guesses, educated and otherwise, welcome in the Comments box. View full size.
UPDATE: As correctly surmised in the very first comments, these are baseball fans. The original caption: "October 3, 1924. Washington, D.C. Waiting in line for tickets for the opening game of the World Series. Picture snapped at 10 p.m. October 3rd, twenty-four hours before the tickets will be placed on sale."