This can be done at Oil Ocean Zone - ACT 2. You have to find a secret submarine at the halfway of the level, enter it and the trophy will pop. There is a point where you can find a fire shield under a little platform and a sea of oil underneath. Go under this platform, and leave yourself to go down (don't worry, it is a secret passage and you won't die). But be careful, because, once you reach the bottom of the level you can die in the oil part.
From the bottom, go to the right side, jumping on the oil, under a plarform and you'll see the little purple submarine full of goodies and a trophy!
To understand better, there is a video guide done by Shadiochao here: