She laughed as she picked up her step after him. Exploring an ice cave that was, frankly, in all probability completely empty wasn't the most daring or exciting adventure they'd ever had...but it was more light hearted than adventures stuck at the mouth of a black hole without the TARDIS, and as much as she loved the TARDIS any adventure was better than just sitting around doing nothing in the TARDIS all day.
Even though their explorations so far really did turn up very little except for endless (and ever darkening) twists and turns and a few interesting ice structures.
Rose was just beginning to wonder if they ought to call it a day before they ended up somewhere without any light at all when the ground she was just stepping on gave out and collapsed downward (into a dizzyingly deep looking chasm) with a sudden crack.