The main passages of the mine tunnels run about 6-7 feet high and 9 feet wide, wide enough for a mine cart to move and have people walking by on each side.  Headroom in active cuts is somewhat less, more dwarf-height or shorter.<br/><br/>The team is able to ready their weapons with little difficulty, considering it's not a crisis situation.  Chay's darkvision operates with or without his goggles or the illumination; for a ways beyond the reach of Cersei's light, he could "see" the contours of the rough-hewn mine walls, the sturdy timbers, the occasional nugget of ore or tool left behind in a shaft.  There wasn't anything moving within the range of his vision, but then again, with the way the sounds echoed against the rock, it was impossible to tell what direction the sound came from.  It could even have come from farther down... or farther up.