This could be a clue... A hole three acres wide and 200 feet deep.
7 seconds sound clip from Batman (1966) - A Riddle a Day Keeps the Riddler Away (S1E11) TV Series.
You can hear this line at 00:17:33 in the Blu-ray version of the movie.
Quote context
[...]
- We'll soon find out. Come on, Robin. Back to the Batcave!
- Gotham City river bending and winding... sections.
- Nothing there. Negative again.
- Hold it. I think we may have something. Let's take a closer look.
- Gotham City Water and Power Plant exact location and size.
- This could be a clue... A hole three acres wide and 200 feet deep.
- I'll bet The Riddler and his gang are holing up with King Boris.
- And at the obsolete Water and Power Plant...
- I don't know what kind of rogues you are, but I demand that you release me this instant.
[...]