I found a 1924 copy of The Mirror of the Sea and recently finished it. It is Conrad reflecting on his sea-faring past, a looking into the mirror and seeing in his weathered face the chart of his life's remarkable journeys. I love how he can comment on an anchor, for example, and weave in his universal musings on humanity. His reflections on various personalities from his past are also moving and convincing psychological vignettes.
As in most of Conrad's writings, perhaps safe to say "all," there is an existentialist flavor to Mirror of the Sea. We live in an absurd and inscrutable universe over which death casts its hue. The Melvillian gravity of his writing is so refreshing in our modern and superficial time.