Bowser in the Dark World
Bowser in the Dark World is the first Bowser level in Super Mario 64. It is a challenging puzzle-like world with many traps and enemies that are nearly guaranteed to surprise you. The trapdoor entrance is behind the star door in the main floor. You will need 8 Power Stars to open this door. Some fans of the game indicate that this and the other 2 Bowser levels(Bowser in the fire sea & Bowser in the sky) have their music to give the player fear. It even stops for one second to give the player fear and is one the best tracks on the Super Mario 64 Soundtrack.
Red Coins are difficult to obtain in this level due to the fact that there are many gaps in the course, but finishing this world alone is particularly easy.
The idea is to grab Bowser by his tail and twirl him into a mine, and when the level is completed he will dissapear and leave you with a key to the castle's basement.