Photo Credit: russ
The Flatiron Building is located in the aptly named Flatiron District at 175 Fifth Avenue, which is at 23rd Street at the intersection of Fifth and Broadway. Even though it is now known as the Flatiron Building, its official name is the Fuller Building, named after George Fuller, who owned the construction company which built it. It was completed in 1902, and at 22 stories is credited as the oldest remaining skyscraper in Manhattan, although the Park Row Building is a few stories taller and was built in 1899. Incredibly, at its' round end it is only two meters wide.
The building is currently a functioning office building, and is home to several book publishers.
To get there on the subway, you can take the Q, N or R train (yellow on subway map) depending on time and day of week, or the 4,5,6 Lexington Ave Train (green on map), but make sure it's not the express train because it won't stop at 23rd. (This is what I've figured out on my trips to NY. If it is wrong please fix! Thanks!)