This is it. You go straight through there until you find a vertical shaft.
3 seconds sound clip from Superman (1948) - Depths Of The Earth (Chapter 2).
You can hear this line at 00:11:37.665 in the Blu-ray version of the episode.
Quote context
[...]
- Probably won't do any good, but I'm gonna try another angle.
- It won't do me any good if the place is guarded.
- Well, that's just it. It ain't.
- Of course, I figured that this ought to be worth a little something.
- This is it. You go straight through there until you find a vertical shaft.
- There's a ladder that leads down to where the miners were trapped.
- Say, I'm from the Daily Planet, I'd like to see the manager of the mine.
- So would a lot of other people.
- So White did hire someone else?
- Only if I get the story, but I'm not so sure of that as I was.
- I'm Clark Kent. And you're...?
- Jimmy Olsen, the Planet's best cub reporter... if I'm still on the payroll.
[...]