catwalk

noun4

1. •
   An elevated enclosed passage providing access fore and aft from the bridge of a merchant vessel.
2. •
   A narrow elevated stage on which models parade.
3. •
   The business of making clothes for fashion shows.
4. •
   Any similar elevated walkway.

   • The lengthening [of the District Line platforms] is being done so that passengers will no longer have to use the narrow catwalks to enter and leave the front and rear portions of eight-car trains. — 1963