A two-roomed building, it is located to the left upon entering the galleria. Inside, one can find a boxing ring on the left and weights on the wall. A counter manned by Danny, is to the right, along with a shelf containing some Buffout and stimpaks.
A door behind the counter leads to the office, where Madden's office terminal can be found, along with an open safe.
Stepping onto the ring before the Grand Reopening will initiate a boxing match with the Champ. Stepping out of the ring during the fight or using any weapon other than boxing gloves will turn the other robots hostile. Boxing gloves can be picked up around the gym for this very purpose. If the Champ is defeated using only the Boxing Glove, the Sole Survivor is declared the new champion and the other robots will go back to idling. Killing them does not seem to affect any of the other robots.
Madden's Gym appears only in Fallout 4.