Underground engine room:- (#8 on the layout map)

Obviously by this time mostly everything inside has been stripped bare. Only a few pipes in the side access tunnels remain. There were from what I could see 4 air ventilation shafts above ground that must have connected to this underground area. On the floor inside the main chamber itself were metal fixing points were I presume the main engine was fixed.

If you want to explore the interior you'll need a torch and watch out for all the debris on the ground..