The group near the hill giants' lair
Assuming you mean ninety degrees inland, rather than toward the ocean.
As the small party tries to evade any possible pursuit, the terrain becomes rougher. No clear path is through the conifers. Fortunately, the harsh climate has left little undergrowth, so it's fairly easy to travel. Unfortunately, the undisturbed snow is leaving clear footprints as they travel. After only a few minutes travelling northeast, the temperature is obviously dropping, as the group gets farther from the relatively warm ocean.
The group in the watery cave entrance
The markings don't seem to be any sort of cryptic message, according to Lyrique's trained eyes. Most likely it's an artistic expression of some sort, perhaps relating the sorts of beasts the obviously primitive artist had seen.
No magical auras are visible - at least in this part of the cave.
As the group moves deeper into the cave, the water becomes more and more shallow, until it's a bare trickle along the floor. All of the water is now fresh water (though doesn't smell especially potable; but it isn't salt water) and the high tide marks have been left behind.
Just as the trio pass the high-tide mark, the cave paintings cease.