There is no Mount Gotham. There's a Mount Sack, a Mount Blank a Mount Gomery, but there is no Mount Gotham.
8 seconds sound clip from Batman (1966) - The Cat and the Fiddle (S2E3) TV Series.
You can hear this line at 00:05:52 in the Blu-ray version of the movie.
Quote context
[...]
- But just what was it she told us before she left us to die?
- Something about an assault on Mount Gotham.
- Why, it's... it's... I don't know.
- Holy Alps! I'd better brush up on my geography.
- It won't do a bit of good in this case, Robin.
- There are man-made mountains in Gotham City's concrete jungle. What's the highest peak?
- Rising a magnificent 102 stories above the city's din.
- What could she be doing at the Gotham State Building?
[...]