This picture is from a 1939 book on automobiles. It's a dyno room with an electric dyno. The big box to the left is the electric motor or eddy current brake, apparently armored in case it comes apart. It's mounted on pillow blocks at each end, with a beam balance in the background. To the right is the test engine, apparently a flathead four, complete with long-stick-shifted transmission.

Note the heavy cast iron bedplate, engine brackets, and pillow block brackets. They literally don't build them like that any more. They couldn't afford to. Also note the racks of resistive heating elements at the top of the photo. By this we can tell the room was located up in Yankeeland, or at least somewhere cold enough you'd welcome 100 KW or so of loose heat to keep you warm. The dyno room must've been lit in a hellish red-orange glow when in operation.