How do you get through these doors in Kingdom Hearts 1?

Alright, there's this door on the hotel, called the "Blue Room", but it is unopenable from the balcony and the hotel hallway, is it openable at all? If so, what is behind it? Also, in the waterways, where you get to the magicians study through one of the doors, there's another one before it, with a big moon on it, how do you get behind it/what's behind it? Thank you for taking your time to answer.