All right, according to this, the time vehicle is sealed off in a side tunnel.

4 seconds sound clip from the Back to the Future Part III movie soundboard.

You can hear this line at 00:10:26.009 in the DVD version of the movie.

Quote context

[...]

- I never knew I could write anything so touching.

- I know. I know, Doc. It's beautiful.

- It's all right, Copernicus. Everything is gonna be fine.

- I'm sorry, Doc. It's all my fault you're stuck back there. I never should've let Biff get to me.

- There are plenty worse places to be than the Old West. I could have ended up in the Dark Ages. They probably would have burned me at the stake as a heretic or something.

- Let's look at the map.

- All right, according to this, the time vehicle is sealed off in a side tunnel.

- We may have to blast.

- Whoa! I think you woke up the dead with that blast.

- Take this camera. I want to document everything!

- This reminds me of the time I attempted to reach the center of the Earth. I'd been reading my favorite author, Jules Verne. I spent weeks preparing that expedition. I didn't even get this far. Of course, I was only 12 at the time.

[...]