Where to find them all Edit
Switch 1: After riding the Zipline, you will be on a log sticking out of a platform (the said platform is also where you get the second secret chest using a nearby Ladder Spear). Drop down on the right side of the platform. You will find an Enemigo with a Harpoon Gun and the first switch.
Switch 2: This one is in plain sight. Just progress normally and you should be able to find it easily.
Switch 3: Also in plain sight. Right after you enter the third section, you will see a brown platform. Drop through it to get the switch.
Switch 4: Easy to find. Once you'll get the halfway-checkpoint, you will see a platform with a Longsword Enemigo on it. There is a platform beneath this one, which has the fourth and final switch to push.
This is a quite strange Challenge in all honesty. Only the first one has any difficulty related to it whatsoever.