I'm not sure if you have to use it on the door as an item or if it opens by itself if you interact with the door. Best to try both.
it worked the next time i tried it ! weird ... im now stuck in the section after the grinding wheel room where there are triggers to push ... ive got 2 of them but the last is blocked by a blue block and theres a bouncing red thing close by that i cant do anything with to interact ... tried the boomerang to hit the trigger but no luck , been all around the stage but cant find anything to help ... any hints ?
really wish there was a walkthrough for this game !
cheers