This is my second diorama , and did so with the intention of it being a supplement to the diorama of the city, the laboratory would be underground and would have access through the hole on the middle of the city diorama . For this scenario polyurethane also use more things to give more details and fill the spaces .... plastic pipes , old appliances parts , empty deodorant , etc ... anything goes ! Sewer wall is just molded foam and plastic tubing used to guide electricity cables in construction, the back wall is lined with a very thin metal plate an old appliance , a little paint here , a little rust effect over there and start, no need to buy materials to make a diorama and have fun in the process, the paint is very basic , some oils with basic colors to mix and have more tones , some cheap brushes , something to glue the walls to the floor and lots of imagination !