[X] Learn to Swim - While you do know how to swim, there is a notable difference between swimming for fun and scuba diving. And an even greater difference when it comes to exploring underwater caves. Dratini would have fun teaching you.
[X] Catch a fourth Pokemon - Catching a Magnemite or other electric-type Pokemon is why you came here, there are almost certainly good options present.
[X] Explore Unorthodox Locations - Exploring parts of the area most people don't will be an interesting experience. Pineco would very much enjoy hiking in the mountains.
[X] See the sights in the Area - While the attractions are limited to the Power Plant, exploring its interior would be rather fun. Chansey would appreciate the more scenic tour. Wait, why are you two here?!
[X] Call Tetsuya - An old childhood friend of yours, the two of you drifted off recently. He recently arrived in Pewter City and just barely managed to earn the Boulder Badge.