I can’t make out what the guy sees, or thinks he sees, in the sky. And thus, whether the racing challenge is directed to that celestial figure or to the child. Is it about reaching shelter before storm conditions catch up with them? Or less on-the-nose?
Maybe patience and the color version will help…
OK, we’ve heard of the Purple Mountains’ majesty…. But I guess the adult is addressing the child, and the joke is in either the non-specificity of the race goal, or in the implausible distance for them to cover?
Comics I Don't Understand 
The goal has to be the mountains, and the joke is that there’s no way that either of them would be able to get there on foot in a plausible amount of time, even if the diagonal stripe in the lower right corner is the beginning of a path.
P.S. Occasionally while travelling I’ve seen a beautiful mountain (or hill) near the side of the road, and I’ve thought that it would be really cool to scamper up to the top to enjoy the view; fully aware, of course, that such a hike would take at least the rest of the day, and would be utterly irrational to attempt.
The guy’s walking stick might be something he uses just for hiking. But there was another recent Bliss with beautiful rolling landscape (and no real joke) and a man standing taking it in while he rests on a cane that seems like he uses it all the time ; and his dog is shown running all over and enjoying the environment.
Yes, it is the implausible distance.
I thought the joke lay in the image itself. When I’ve seen pictures like this, of an older person who is clearly a parent or some adult figure in a child’s life pointing off into the distance, there is no caption. We are just left to assume that the adult is imparting some kind of wisdom, or exposing the child to the wonders of nature for the first time. A touching, tender moment.
Nope. It’s a race.
Here’s the one I meant. It was from just the day before. The tremble lines around the old man make it clear he needs to go slowly and needs the support of the cane. But he can enjoy the dog’s enjoyment! I think the weird thing in the air is a falling leaf, not a bird.
Some parents insist on rubbing it in.
I thought they were on a flat clifftop looking down on the road, so the kid would run off the edge. Not sure what that inkblot says about me.
I thought they were standing on a flat cliff, so the kid would run off the cliff. I don’t like what that inkblot reading says about my brain…
Oops.
In the gray-scale one, I couldn’t tell if the intervening distance was land or water, but otherwise, it just looked like your average dad joke.
I’m re-reading “Lord of the Rings” by Tolkien, and everyone spends a LOT of time looking at mountains in the distance, and walking to mountains in the distance, which always takes many days, and sometimes going into mountains. And I’m only on Page 300. There’s another mountain at the end, but I think we are going to see lots and lots of mountains between here and there.