In Emerald and FireRed/Leaf Green there is a battle facility known as Trainer Hill or Trainer Tower. It is a place where you battle trainers. There's 4 floors in both, with increasingly more difficult Pokemon as you continue. You are also timed in here. If you get to the roof, you'll get an item. Also, in the FR/LG version of this area, some trainers have shiny Pokemon.
Did you ever bother with the Trainer Hill/Trainer Tower? I did once. Seeing an NPC with a shiny Pokemon freaked me out a bit at first.
I never really bothered with Trainer Hill/Trainer Tower much when I was younger, but in a Fire Red play-through I did recently, I decided to get to the top just to see what would happen, I wasn't overly impressed with the reward. I feel like they could have done more with it.