catwalk

n. 1. A narrow walkway projecting from a stage into the seating area of a theater; it is used, e. g. by models displaying clothes on it at a fashion show. Called also runway. [ WordNet 1.5 +PJC ]

2. A narrow walkway high in the air to allow workers access to parts of a structure otherwise difficult to reach. Catwalks are located, e.g. above a stage in a theater, between parts of a building, along the side of a bridge, on the outside of a railroad car, on the outside of a large storage tank, etc. [ WordNet 1.5 +PJC ]