Considering the amount of time Ransom spent in the sea in Perelandra, I would not be surprised if Lewis had the occasional swim. Maybe he was not a sportsman, and I don't know much of his personal life, but he was child at some stage
![blush :blush:](./images/smilies/blush.gif)
And to have the imagination he did, he must have done some awesome things as a kid!!!
It seems as though he really got involved and saturated himself with the things he wrote about. He knew them on a different dimension. It is almost as he had somebody working on the 'inside' of all the different worlds that he wrote about.