Amid all the cute beaver plaques that adorn the Astor Place station lies a subway mystery: What’s with the tiled-over doorway on the southbound side that says “Clinton Hall” above it?
Turns out it was the name of the building at 13 Astor Place, above the station. Formerly the Astor Place Opera House (and the site of the Astor Place riots in 1849 that killed 20 people), the building housed the Mercantile Library of New York. When the city constructed the Astor Place station in 1904, they created an exit from the platform to the library.
The Mercantile Library occupied the site from 1855 to 1932, when it relocated to 47th Street.