Super Hydlide/Secrets

Free Experience
In the ../Forest City/, there's a lake in the center of the town with a bridge going across it. Go to the bottom edge of the lake, directly left of the bridge and "use" any unit of money (you won't lose money by doing this). Exit the menu and check the ground to get 30 Experience points. Repeat as much as you like.

Sound Test
From the ../Forest City/, head left to reach a small building. Step inside to access the Sound Test.