The oldest Irish Bar in NYC, McSorley's Old Ale House, located at 15 E. 7th St. right near Coop Union, is a must see. They only serve two drinks, light and dark ale.
It opened in 1854, women were not allow in until 1970. The bathroom doors were made of transparent glass. After 1970, some sort of non-transparent glass was placed over the doors.
Sawdust is still spread on the floor, and nothing has changed since 1911 (except the bathroom doors).
I remember when you had to but two mugs of ale at a time. They are also known for their cheese and raw onion platter.