“Here’s a chimney,” Jill said. “A big one. And some kind of iron furnace.”

Ben guessed that the brick chimney was about twenty feet from the southeast corner of the basement. It measured at least four feet on each side, and the brickwork rested on four large granite blocks. Bending over to shine his light directly at the floor, he was surprised to see the surface wasn’t concrete—more like a mix of sand and dirt and crushed seashells, packed tight and flat.

Robert said, “I think I’d call that thing a stove instead of a furnace—looks like it burned wood. Yeah . . . see? White ashes—definitely a jumbo-size woodstove.”

Ben was adding the chimney and woodstove to his drawing when Robert gave a low whistle, and said, “What is that?”

Ben followed the beam of Robert’s headlamp. A large round tube hung from the low ceiling, and it ran twenty or thirty feet to an enormous domed structure. More big tubes, at least ten of them, seemed to sprout from the top of the dome.

“We had one just like that in the basement at our house,” said Ben, “except about ten times smaller. Same thing, though. My dad called it an octopus furnace. This stuff we’re seeing? It’s all from different time periods—the woodstove probably came right after they stopped using the upstairs fireplaces. Then they burned coal under that big octopus dome. And look,” he added, aiming his headlight upward at the black metal pipes hanging from the ceiling beams, “those pipes come from the boiler, the newest heater. And the boiler sends hot water to all the radiators in the school.”