During the tunnel's construction, an alignment underneath Central and Queensbridge Parks was decided as the only feasible route for the tunnel. Because the 63rd Street Tunnel is at such a deep level, there are several ventilation shafts along its route. In Central Park, near the Central Park Zoo, there are several ventilation grates that are at the same level as the ground, covering about of surface area. A ventilation building was deemed to be architecturally unacceptable, hence the inclusion of several grates. On the other hand, gratings at Queensbridge Park were declared to be unfeasible due to the park's small usable area. Therefore, a ventilation building stands in Queensbridge Park, measuring . Additional ventilation shafts are located at Second Avenue and 63rd Street in Manhattan, and on the western shore of Roosevelt Island. When the 63rd Street Connector was constructed in the 1990s, additional ventilation structures were built at 29th and 39th Streets in Queens.