Well, since all of the overland routes have been egg-xpunged, the only way to go is underground.
10 seconds sound clip from Batman (1966) - The Yegg Foes in Gotham (S2E14) TV Series.
You can hear this line at 00:21:06 in the Blu-ray version of the movie.
Quote context
[...]
- I'll make you a good deal. Better than wholesale.
- Why, do you realize that if I paid one penny, it would ruin my reputation among my peers?
- It's almost dark, Egghead. Don't you think we better get going?
- Hey, how are we gonna get out of here anyhow? They blocked off the airports.
- Well, since all of the overland routes have been egg-xpunged, the only way to go is underground.
- So let us explore Gotham City's sewer system.
- Just the right place for a rat like you.
- The only place you're going is up the river.
- Let's give them a taste of our knuckles, shall we?
- All right, all right, that's all. Cease and desist. I'm done.
[...]