Information about this lot
You can use this form to suggest uses that the community actually wants to see as concessions in this building:
NYC Parks will consider your fantastic ideas and you should also share them as notes below and become an Organizer so you can connect with others to make the futures we imagine real! Keep in mind that NYC Parks isn't going to do your project for you.
Opening buildings costs money and NYC Parks' has a limited budget. Here is a great guide to how to get money for your NYC Parks building stewardship project, created by the Center for Urban Pedagogy, New Yorkers for Parks and Partnerships for Parks: http://welcometocup.org/file_columns/0000/0613/improve_my_park.pdf. Follow the tips for "Capital Projects."
Getting your Council Member on board is key: they have money to give out every year via their discretionary budget; some Members allocate some of their discretionary money to Participatory Budgeting: https://council.nyc.gov/pb/. You can get involved to get the word out about the need to re-activate the building you want to steward.
The building might be landmarked. If it is, any work will need to comply with these rules: http://www1.nyc.gov/site/lpc/applications/applications.page
What's behind the door?
I assume its locked.
Its beneath the Highbridge Skatepark.
Its seems to be in use because this Google Street view above does not have a light above the door, but a photo taken on 12/18/2016 distinctly shows a light.
The mystery may be resolved by this link http://beyondcentralpark.com/BCPHighBridgePark.html
Read starting at 'A couple of Historic "Artifacts" of Interest to the Runner' and "the Shaft 25 Retaining Wall" which is supposed to be part of the New Croton Aqueduct.