Behind the Falls
If you want to get wet
That's the way to walk closer to the falls.
We didn't do it (it must be fun, but time was short and we had to choose), since the Maid of the Mist, took us even closer, with less sacrifices, and gave us the chance to see the lines going up and down by the water, seeming a strange ritual.
Jet Boat Rides
I skipped Whirlpool
No I didn't make the jet boat rides.
Seen from the air, the whirlpool seems really challenging and, merging my good memories from Safari Macuco in Iguaçu,
Brazil, with the comments in VT, I think that, next time in Niagara, I'll forget that I'm over sixty, and...
Though you may have good views from the top of one the towers facing the falls, I strongly recommend a flight over the falls.
There are helicopters continuously up and down, with trips that take about 10 minutes, showing a small extension of the river, but including the falls from several angles, and the whirlpool.
Not cheap ($108 for an adult, I think), but...