I'd noticed that 171 was a moderately sized cave on the plateau that was unsurveyed, so decided it was a nice job for a rest day. To make life easier just took helmets, clothing and survey kit. We'd spent the morning successfully recalibrating the distox2 inside the bivi cave. Started at 171a and surveyed to 171b - a nice phreatic passage with multiple skylights. A low bit in the middle. Continued a bit beyond the "b" entrances, but decided to return to finish with oversuits.