The third, and most modern type of water level indicator, called a sight glass, is a pipe open at the top and bottom to the interior of the boiler. The sight glass is a heavy glass window set into the pipe through which the water level can be viewed. The passageways outboard of the boilers are lined with storage and shop compartments. These compartments are believed to have been added in the 1930s when Belle began making extensive excursion trips. The last two side compartments aft extend beyond the rear of the boilers.
Passengers can walk from the bow aft to the engine room by way of the passageway to starboard.
In the engine room they can ascend to the deck above on the stairway at the stern bulkhead. The engine room occupies the entire width of the stern and contains the engines, rudders, auxiliary machinery, and engine controls. The engines are mounted to port and starboard in the engine room on massive structural members called cylinder timbers. The cylinder timbers support the cylinders and crossheads at their inboard ends and the paddlewheel shaft at the after end. The engines were transferred from another steamer to Idlewild when she was built.