Ron Winter served as one of the Queen Mary's junior engineering officers when she set sail in May 1936. His memoirs are fascinating, and he chronicles ship life in a masterful way. Winter describes what it was like to work in the Queen Mary's various machine and engine spaces (the subject for future posts).
In this particular passage he describes the ship's long tunnels:
From the After Engine Room ran the tunnels which carried the [propeller] shafts from the engines, way under the stern of the ship. These shafts were supported every few feet in bearings, and a gangway ran down through the tunnels so that these bearings could be inspected, and also the stern glands where the shafts passed out through the ship's bottom into the sea. The tunnels were well lit and very much cooler than the engine rooms, and in very hot weather it was a pleasant change to work down there. The sight of these very long and enormous shafts - 2 ft 6 in in diameter - turning away was very impressive, though the tunnels were rather lonely places and you were conscious of being hundreds of feet away from human company.
These spaces still exist on the Queen Mary walking tour today and - although the propeller shafts have been stopped for 44 years - are still rather impressive. They are pleasantly cool too, just as Winter describes, as well as lonely.
References: C.W.R. Winter, Queen Mary: Her early years recalled (Wellingborough: Patrick Stephens, 1986), 97-99.