The famous waterfalls of Mussoorie are Kempty Falls. They're totally commercialized now with maggi shops all around the base of the falls. With over 300 steps to get to the base, the hike back up could be tiring. There shops selling local nicnacs all through the steps.
You could dive in the falls with appropriate swimwear! The water was freezing cold in March when I visited.
Kempty Village has a wall of hope made out of plastic waste. If you find it like I did, it's worth your IG shot!