PEABODY - It reminds Mayor Michael Bonfanti of the old TV program "Let's Make a Deal." There's door number one. Door number two. And door number three.

The mayor drives past all three as he heads home from work each night on Lowell Street, reaching the Route 128 underpass.

But don't ask him to pick one. Even he isn't sure what's behind any of the doors. They could be the entrance to secret bunkers in the war on terror. Or the hideout of Whitey Bulger. Maybe the start of that tunnel under the Cape Cod Canal.

"It's where we keep all the money," jokes John Lamontagne of the state Highway Department. In fact, MassHighway holds the key to the mystery. It's the department's space, spokesman Erik Abell said, adding that there's nothing exotic in there, just a handy space housing "materials."

Of course, you'll have to take his word for that. No one is allowed a peek inside, Abell said. "For security reasons."

Beneath the constantly busy highway, alongside hectic Lowell Street, the three massive, garage-style doors are constructed within the poured concrete bridge abutment. In addition are three opaque windows and a walk-in door.

John Brennan lives in view of the doors, on Lowell Street. He's been in this neighborhood a long time. In fact, he was there when they built the highway. But he hasn't noticed any activity for a long time.

"I haven't seen the doors open since 1952," he said. And when asked what might be in there, he shrugs. "No idea."

Not that Brennan worries about it.

"Look at the bird droppings," he said, "and that'll tell you which doors they open the most."

On the other side of the highway, Kosma Evangelides also shrugs when asked what's behind the doors.

"Storage, I imagine. But I have no idea what kind of things are in there." He glances doubtfully in the direction of the doors. "I don't know if it's something corrosive. I doubt it's contraband."

Beyond his assurances that it's only "material," Abell advises that some equipment is also stored behind the doors during the winter. A similar storage area exists elsewhere in the state - although he doesn't mention where.

The mystery behind the doors can be easily solved without state help, however. Vandals have broken some of the windows, affording a clear view of a cavernous space, extending about 25 feet back. Stacks of lumber are stored here, along with barrel-sized green drums - of something.

Bonfanti isn't worried. The state is expected to notify the city if anything hazardous is left in there.

"The doors were open the other day when I went by," he said, while conceding that he didn't get a good look inside.

Just in case, fire Chief Steve Pasdon said, he's going to check up on the contents of those drums.