The view of the Sumidero Canyon from the top is really beautiful. You get an idea of how high and how big the canyon actually is. It’s really cool. Apart from that, you can see the motorboats travelling along below – the ones you were sitting in just before.
I was there on a tour myself. The viewpoint was our second stop and the stop directly after our speedboat ride to the famous point where the rocks rise up so beautifully. I don’t know if you can get to this viewpoint on your own. However, I suspect that something is driving along there. It’s right next to a road. However, I don’t know how long the journey takes or how much it costs. So unfortunately I can’t tell you whether it would be worth travelling there without a tour or not.
But I can tell you one thing along the way: The boat tour on the canyon is an absolute must. The viewpoint is a very nice on top. But I would only go there if it’s not too much trouble or with a tour.