itch.io

IMO it's important to find a balance between controlling the order in which players discover stuff and giving them some choices that at least feel meaningful. You might perhaps give the sites descriptions like "A river delta," or "Rocky foothills" perhaps with some hints about what's there or why those sites were chosen ("suspiciously linear rock formations" or "a small but fresh-looking crater"). If you put the third one closest to the extraction point, they'll probably go there last and maybe it doesn't matter what order they do the first in. And then the bunker could become visible when they climb the foothills, giving them an optional side trek.

There's also the sneaky option of making certain important things discoverable at any location or guaranteed to be at the first one they go to. You don't want to overdo that as eventually the players will figure out that their choices are an illusion, but it works well if used sparingly for plot-essential things.