Use a photo of the Gym from any number of books (eg. Illustrated History) as a reference. 

Step 1 (adding the flooring and tile marks). UPDATE. The floor of the gym was tiled. Use Evergreen planked sheet plastic for the Gym floor. Score lightly cross wise to the same width as the planks to create the squares . Cut it to the dimensions of the room and glue it down plank side up. Then paint black diamonds at each point where the lines cross, see any Gym photo reference. Photo of Dan Cherry's Gym interior.

Step 2 (adding the bow and port walls). The bow wall is added during the construction of the Grand Staircase (See GRAND STAIRCASE section). Add the port wall of the Gym from the stern Gym wall up to the wall that you created for the aft side of the Grand Staircase foyer. Measure the distance (approx. 39mm x 7.5mm) and cut out of sheet plastic. Dry fit until you are satisfied and then glue into position.

Step 3 (making the map/ship schematic display). Cut two panels from the 2 bar (part C20) A/M railing kit. You should have 3 horizontal rails and 3 posts. Now cut a piece of sheet plastic strip to fit on the bottom half of these two panels from the floor up to the middle rail. Next cut a piece of Evergreen plastic strip 9mm long 1.5mm wide. Cut this in half to 4.5mm long. Now glue these two sections side by side on to the top half of the two panel railing above the single strip already in place. The world map is to be painted on the the left panel (with the piece facing you) and the Olympic class vessel on the right. Use black paint and a super fine brush to paint a tiny world map and the silhouette of an Olympic class liner. Glue this assembly to the center of the port wall of the Gym.

Step 4 (making the cupboards). Use plastic sprue stock from the tree and sand it into a rectangular shape about 2mm x 3.5mm using the sanding block . THEN cut this to a length/(height) of around 4mm. This was glued to the port wall in the corner near the bow wall.

Step 5 (painting the room). The lower section of the Gym walls were clad with wood paneling. Paint the lower 1/3 of the walls with Testor's Model Master Wood including the cupboard, map base and inside door that led to the foyer into the Boat Deck's Grand Staircase reception lounge. Paint the inside of the exterior door dark brown (see the Jack Futrelle photo). The top 2/3rds of the walls are left natural white.

Step 6 (adding the pillars). Approx. 1/3 distance from the port wall of the Gym were the roof support pillars. Cut these from either pulled sprue or microrod to 9mm in length and set aside. Next make two equal pencil marks width wise (approx. 10.33mm). This will divide the room into thirds. Use a perpendicular line from the port mark for the next section. Next make three pencil marks along the floor dividing the distance from bow to stern into quarters (approx. 9.75mm each). The 2nd (middle) pole went in the center of the Gym and the other two poles in line halfway between the middle pole and either the bow or stern Gym wall. These were painted to match the lower 1/3 wall brown.

Step 7 (adding the stationary cycle's wall board). UPDATE. On the port wall between the central map/schematic charts and the cupboard in the port/bow corner was a circular gauge contained in a large square wallboard. At a quick glance it looks like some modernistic clock (compared to the rest of the decor). This was as tall as half the height of the gym and sat on the wall directly in front of the stationary cycles. It attached to the wall so the bottom sat flush with the top of the brown section of the wall. Fashion this out of sheet plastic about 4.0mm x 4.0mm. Apply a circular band of yellow paint touching each of the cardinal points (center of each edge). When dry use paint a solid circle dark blue circle in the center with a diameter of 3mm. This leaves a yellow ring with a blue center and the corners still white. Next take a fine brush and paint each corner dark blue, working in towards the yellow ring being careful not to paint over it. When the blue has dried add the two colored dots (one red and one white) in a random position on the ring or use the positions suggested by Ken Marschall in his cutaway painting in Inside The Titanic. Glue this to the wall as described above.

Step 8 (adding the two stationary cycles). This fix assumes that you have replaced the crane booms with the GMM parts. Build the frames from by cutting out 2 of the largest 'X' of the crane booms. Build the wheels by cutting 2 microdots of thin sprue. Glue the microdot to the bottom of the 'X' piece. Create the cycle bases by cutting two small sheet plastic rectangles then glue one cycle per base. Create the handlebars by cutting two 2mm lengths of extremely thin pulled sprue and gluing them perpendicular to the top most forward arm of the 'X'. Paint the cycles black and their front wheels one red (right cycle) and one white (left cycle). Finally glue side by side facing the circular wall board.

Step 9 (making the rowing machine). Make this out of a piece of scrap plastic sprue glued to the floor in the same position seen in the Titanic photos. Make the rowing arms out of 3mm long thin microrod or pulled sprue and glue two aside down the rowing machine's main frame. The unit was painted dark brown.

Step 10 (making the electronic horse). To make the body by sanding down a length of sprue stock into a rectangular shape about 4mm tall x 2mm thick x 3.5mm wide. Then attach a small pulled sprue pip to the top of this to represent the handle. Make the saddle by taking round sprue and sanding the bottom and two sides flat leaving the top round. Cut this to a length of about 3mm and then glue to the side of the upright rectangle. Glue this to the floor by the 3rd and 4th starboard gym window aft of the gym door. Paint Model Master Wood. Note: This is all of the gym equipment we made as it is hard to see in the windows. There were some more mechanical devices toward the stern end of the gym as well as a speed bag hanging from the roof near the doors and port bow cupboard. Dan Cherry suggests that you drill out the door to the gym to see any details you put into this room and reward the effort you put in.

UPDATE.

Overview photo of Gym, GSC and Marconi Room by Dan Cherry.