This is the final room of a level called The Solar Express, from the Strawberry Jam mod.
This level absolutely ROCKS!! This my new favorite level in the entire mod; possibly even the entire moding community. The music, the visuals, the story, the gameplay, everything is just sooo well done. Once I finish the grandmaster lobby, I'll have to do another runthrough of this level to get all the strawberries.
I'm on a mission to complete the grandmaster lobby by the time I graduate from college, which is in about a month from now. 6 levels remain, including the heartside. Wish me luck!