Diving as a Hobby is party art, party style, but mostly just showing up!
In addition to being the building required in order to pursue the Diving Hobby, the Community Lot called the Swimming Center is also a place you can have your Sims congregate and cool-off on a hot Sim day, swimming, diving, and splashing around, drinking beverages, and singing songs about the Australian Girl they met at the beach last summer and... Hey! It could happen!
Seriously though, when your Sim arrives at the Swimming Center they can choose from the following Sim Actions:
- Beverage to GoGo: Espresso (30s / 9 XP)
- Beverage to GoGo: Double Shot (1m / 12 XP)
- Beverage to GoGo: Fancy Coffee (5m / 15 XP)
- Bumpy Ride Slide: Use Slide (7s / 10 XP)
- Chair: Ponder (2m / 15 XP)
- Chair: Reflect (4m / 30 XP)
- Chair: Speculate (8m / 60 XP)
- Diving Board: Brief Leap (4m / 15 XP)
- Diving Board: Aquatic Lunges (1h / 150 XP)
- Diving Board: Disciplined Dive (9h / 450 XP)
- Diving Board: All-Day Dive (1d / 900 XP)
- Kiddie Pool: Play in the Kiddie Pool (3m / 16 XP)
- Kiddie Pool: Make Splashes (1h / 72 XP)
- Kiddie Pool: Play Pirates (3h / 300 XP)
- Lifeguard Chair: Guard Pool (3m / 45 XP)
- Lifeguard Chair: Supervise (8m / 72 XP)
- Lifeguard Chair: Enjoy View (25m / 130 XP)
- Pool: Go Swimming
- Toilet: Use the Toilet (30s / 12 XP)
- Trophy Case: Appreciate (4s / 7 XP)
Chances are this will be one of the latter buildings you construct in your game - but if the only reason you are building it is to do the Diving Hobby, you may be better off checking on your Neighbor's Towns to see if any of them have built it, since you can use theirs while visiting to level up the hobby.
If it is a choice between building the Competition Center and the Swimming Center and one of your mates already has the Swimming Center, I would go with the Competition Center hands down since you can use your mates Swimming Center but you can only use your own Competition Center. Just saying.