That's OK, because Walter has heard enough to know where the tube with the plans are: "The subway platform beneath Newark-Penn Station in the wall." It's because, as a boy, his most prized possession was his collection of Detective Comics and since he, like everyone else, was "terrified that the pinkos would attack," he hid them in the safest place he could think of: underground.
But, as Etta points out, every major access point to Manhattan has an Observer checkpoint, guarded by both Observers and Loyalists and she doesn't know if they can even get close enough to take them out without being detected. Olivia says they'll need to create a diversion, and Peter thinks they'll need much more than that. Walter says they need to get into a rolling cabinet that's in the amber. "Walter, there's nothing in there except lab equipment and your Easy-Bake Oven," says Astrid. Walter says, a little snippily, it's what under it that he wants.
So let me get this straight -- there's more underground space under this lab? They open a hatch, under which are some stairs down to some sort of subterranean chamber. Walter won't just tell them what's down below, because he's "not sure what's left."
They get down there -- the place has its own still-working electricity that Walter flips on -- and find a cobwebbed room that looks much like Walter's lab only darker and creepier: it's his cold storage of all the Fringe events they have ever encountered, dormant for twenty-one years. If they're going to find a diversion to get into the railway station, they'll find it here. "There was a time when we solved Fringe cases. Now I think it's time we created a few of our own," he says. Now there's a line worthy of an ad break if I ever heard one.
So Fringe has really opened up the prop vault for this scene, with all manner of creepy gadgets and souvenirs on display, although I really doubt A) Astrid having no idea about this place (even though her line "I wouldn't have slept at night if I did") and B) the FBI not wondering why, say, PORCUPINE MAN isn't in some kind of special evidence locker somewhere.
Walter explains he kept all this stuff: No. 1 because they're his and No. 2 because he has a "healthy distrust of the government." Which is fine, but given how many Fringe cases involved some psycho carrying on his work, you'd think he might be a little less cavalier about having so much weaponized creepery in one place. Especially if it's stuff like the hair-trigger amber-device-that-looks-like-a-walkie-talkie is just lying around unsecured for someone like Etta to pick up and almost encase them all.