Columbia subject headings:
Allegheny Portage Railroad National Historic Site (Pa.)--Buildings, structures, etc.--Conservation and restoration.
Tunnels--Conservation and restoration--Pennsylvania--Allegheny Portage Railroad National Historic Site.
Harvard subject headings:
Princeton subject headings:
Allegheny Portage Railroad National Historic Site (Pa.)
Railroad tunnels--Pennsylvania--History.
Tunnels--Pennsylvania--Design and construction--History.