Only the most hardcore of insomniac tunnel running foamers will ever have a chance of knowing what the hell the Sea Honk is. To be fair, there’s very little evidence, and it’s spread somewhat thin around the entire subway system.
All of that said, what you’re looking at is a mystery set of stairs, connecting two very separate subway tunnels which were built at very different eras, decades apart in fact. Why they were built is as much a mystery as the existence of the Sea Honk.
What is known is why it was sealed: up until the 1990s, the tracks in this part of town were a haven for homeless people. These stairs provided another route for the homeless to access the tunnels undetected.