Q: Context: Castle Clinton or Fort Clinton, previously known as Castle Garden, is a circular sandstone fort now located in Battery Park, in Manhattan, New York City. It is perhaps best remembered as America's first immigration station (predating Ellis Island), where more than 8 million people arrived in the U.S. from 1855 to 1890. Over its active life, it has also functioned as a beer garden, exhibition hall, theater, and public aquarium, and currently is a national monument.

Question: where did immigrants enter new york before ellis island? Let's give stream of consciousness first:
The relevant sentence in the passage is: Castle Clinton or Fort Clinton, previously known as Castle Garden, is a circular sandstone fort now located in Battery Park, in Manhattan, New York City. It is perhaps best remembered as America's first immigration station (predating Ellis Island), where more than 8 million people arrived in the U.S. from 1855 to 1890. Therefore, the final answer is Castle Clinton.