Marathon Swimming and Rock Climbing
It's interesting to explore similarities and contrasts between marathon swimming and other endurance/adventure sports. Mountaineering is often discussed; and there was a popular thread here on the Barkley Marathons and ultrarunning.
Rock climbing is another spiritual cousin... and in the news lately after Alex Honnold's first "free solo" ascent of El Capitan in Yosemite. Some have asked what the marathon swimming equivalent of this would be.
Anyone interested in learning more about climbing - its culture & cast of characters - I highly recommend Valley Uprising:
Also available on Netflix.