These kinds of tunnels were old, from back when Manehatten was still a walled city, and there weren't many of them left. There might not even have another exit that remained unblocked, but Handy was desperate. Navigating was a bitch but he managed it, trying to avoid going down as much as could be helped. He saw one stairway descend into solid ice. If it turned out there was a lower level, it was likely going to be even more inhospitable than the surface.