Super Mario 64/Vanish Cap Under the Moat

This course can be found in the moat. You must drain it first. Go in to the basement of the castle. Follow the circular hall, and go through the door. Follow the wall on the right until you hit a wooden door. Go through the underwater hall, and you will find a room with two pillars. Ground-pound the pillars and the water will drain. Go out the newly exposed door, go right, and you will find a hole in the ground by the waterfall. The course lies through there.

Finding the Switch
Once you enter the course, you will be given a Vanish Cap, however, it is useless on the slope. Go down the slope, ride the platforms, and there's the blue switch. Now you can become Vanish Mario, and slip through cages and ice without even having to try!

Red Coins
The first four red coins are found on the slope, so try to slide carefully onto the platforms. If this is too difficult, you can crawl on the slope without falling off. The other four coins are found on or near the rotating elevators, so jump carefully.