How do you get a power plant in super Mario 64?

Answer 1

You have to find the secret switch inside the castle, and make all the ? blocks solid. They sometimes contain a power plant. To find the secret switch, stand on the rug where light shines through the sky light, inside the castle. Now, zoom in the camera, and look directly at the sky light. Mario will be given his wing cap. Steer him to the tower with a red button and a ? block. Jump on the red button. The ? block will become

solid, along with all the others in the game. Now, just simply jump off the tower. Done!