Yes, it's the Yoshi Level! By beating this level, you can ride Yoshi!

You're back in the beach outside the park. There are turtles before the flowers. Water each turtle, antagonize it until it flips over (on the sand somewhere so it gets stuck) and then stomp it. Do it in the sand so they sink in. Get all of them and you get a shiny. This level is very quick, because you also now have to do the yoshi-egg-chase in the center area.

Tip from eriK:
spray the sand in the sunflower area with your FLUDD - ignore the coins and the fruit. when the sand sparkless when hit by the water - continue spraying at that point, a blue crown will appear and you'll get a blue coin. I've found two of these.

Super Mario Sunshine Walkthrough