Sorry, didn't know that the official imaginary gym creation police were going to be doing an inspection of this topic.
Nobody expects the official imaginary gym creation police. Amongst our weaponry are such diverse elements as: fear, surprise, ruthless efficiency, an almost fanatical devotion to N, and nice Team Rocket uniforms.
My NIDOKING brings all the boys to the yard: http://goo.gl/ExAoe
Levels would be between 32 and 35 (roughly), meaning I'd likely be the 5th or maybe 6th gym. I'm not a fan of gym gimmicks, so I would probably just stick with a basic maze or maybe a trivia contest like the Cinnabar gym. Most importantly, it would be possible to reach me without facing a single other trainer if you didn't want to. As for the badge, I'm thinking something like the "Armour Badge" or "Iron Will Badge" (lame pun, I know...).
Another day successfully wasted. "I'd rather die than go to heaven" - William Murderface