As correctly noted, the green door is located on the south side of West 15th Street between 8th and 9th avenues, at No. 346 to be exact. The "antiques" sign is outside 344 W. 15th, home of an eight-room B&B called Chelsea Mews Guest House. Both buildings date from around 1900.
· Curbed BuildingSpotter: Antiques in Chelsea [Curbed]