Exploring Neptune (Dreams #1)

In my dream, twin sisters I once lived by were suddenly transported with me to Neptune, and somehow we acclimated to the new environment and were able to explore what no humans had seen before. At first, we stuck closely together, but while I was distracted by a beautiful alien artifact they suddenly darted into a dark cave, as I followed I slipped and fell into the darkness, just as I felt the solid bottom of that fall rapidly approaching I was mercifully awakened from my slumber.