Swimmm... like a fish? 50m pool. My favourite. Although, makes for difficult sprints... tiring, but a good mental push. Swam 10x50m front crawl, 10x50 flutter, 10x50 crawl, 10x50 flutter/backstroke, and then 50x5 sprints, with 50m intervals inbetween... worked out to be 50x50m in total. Good swim, good swim indeed.