So, one of the game elements in Lone Spelunker is the fact that you can't just go hammering pitons everywhere. The game "channels out" certain portions of the background to represent space, and wherever it has channeled out this space, you cannot hammer pitons.
This is a game mechanics concession to add some challenge to the game, but it's always seemed a little...flat. I've also been worried about whether it is conveyed visually well enough.
Well, I think I have solved that by adding a parallax effect to the channeled out area. Now, as you move, it's clear where there is stone to hammer into, and it's clear where there is nothing but space beyond. You can see what it looks like in the screenshot here. (Light levels bumped up to make the parallax effect more prevalent.)