Being held captive is destructive to a person's mental state, no matter how nice their living situation is inside the gates. Many POWs suffered from what would become known as "Barbed Wire Disease," which led to mental breakdowns or suicide attempts. In order to avoid this, the POWs had dozens of ways to try and stave off the boredom, monotony, and stressful uncertainty of their confinement.
Active outdoor pursuits were favorites, with gardening and sports taking up a lot of the men's free time. Volleyball, tennis, handball, football, and more were played casually on any day, but there were also sports competitions planned well in advance that were taken extremely seriously. As one commandant explained in an official report, the "prisoners prepared themselves for the meets as though to contest with the champion athletes of the world. Every event was hotly contested" (via The Annual Report of the Secretary of War). The winners of these competitions even received prizes.
There were plenty of more intellectual pursuits as well. Fort Oglethorpe had enough world-class musicians and conductors confined there to hold regular concerts. Some of the prisoners started producing their own newspapers. A camp university was founded, and the professors who'd been lecturing at schools like Harvard and Yale before their arrests taught classes that were very popular with the prisoners. Every week there was a movie night, but the Germans also got into acting themselves, building a stage and putting on several performances of modern plays.
