A shaft of light occasionally comes down from above, but much of the time we are in sunless corridors.
June 1962
In winter, the pools are cool.  A wetsuit helps us keep warm.  Too warm if we have to work hard at breaking through ice on the surface.

But these deep, narrow side canyons are, in winter, generally much warmer than outside; they are like caves, where the surrounding rock holds the temperature rather constant.

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Dec 1962