This stage is Spike’s Lost City (4-5). This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars.
Game Play Walkthrough Video
Green Star 1
Take the first green pipe you come across. Turn on all the blue switches to yellow to get the Green Star. Consider kill all the spike logs enemies to make your quest easier.
Green Star 2
At the place where three enemies are tossing the spike logs. Use Cat Mario to climb up a huge arch wall and walk a bit to claim your second star. This star is easy to miss so watch out for it.
Green Star 3
The last star can be found at the place where the platforms tilt. You will have to jump carefully to get to it.
The stamp is found near the first green star. It’s on arch bridge to the left.