It was occupied by a series of hospital facilities not so long ago. There was a VA facility just under the 59th Street Bridge, which was accessible by an elevator from the bridge walkway.
Once development started, nearly every inch of the waterfront was taken over by bulky apartment buildings.
I am not a student of Roosevelt Island, but I think they were mostly coops. There is a short bridge to Queens on the eastern shore. A tram and a subway line go to-and-from Manhattan. These are met by a bus that circumnavigates the island.
It’s a dense landscape but a pleasant view from the East River Esplanade.
Walk with Me, Too 