Non molten tunnels
The backup story here is far easier to find than the others. While the other story is mostly forgettable, the Supergirl story features an early appearance of the Legion of Super Heroes. The story is not particularly original, it rehashes a lot of the plot (and even two specific locations) from the first appearance of the Legion members, though this one adds a few more new Legion members to deal with. While the story is similar to the first, this one is a lot more polished, still rooted in the golden age, but with a more refined approach to the story telling (though admittedly still focused on children). A better story than others so far in the Legion timeline, but still has some distance to catch up to modern tales.