In relation to both paths - both paths do lead upwards. Also, the higher up they get, the colder it gets and clearer it becomes that both paths must open up to the cold upper reaches of the mountains.

The larger one that the onix can traverse through slopes up at a gradual rate, and a little more than half way up the path there will start to be numerous sounds of what is clearly fighting off to a chamber to the side. Sounds of rocks falling, and numerous noises of battling pokemon. They can choose to go investigate this, or ignore it.

The smaller path Imogen started off on is much steeper, and therefore more direct - it gets colder faster, but it also becomes increasingly narrow. Where the opening do it could fit a human through it with effort, closer to the other end of it, it becomes much to small for anything much bigger than a small pokemon to fit through it. There also is nothing much else of interest down that pathway other than the before-mentioned entrance to the upper levels of the mountain