Billy Groman  age 10 for his question:

How far is 20,000 league?

A league is a measure of distance. But  for a long time  nobody seemed to be sure how long it was. The fairy‑tale giant wore seen‑league boots. That was a poetic way of saying he could take tremendous strides. The exact distance was not told.

Nowadays we take a league to be about three miles  on land or sea. So 20  000 leagues would be quite a distance some 60,000 miles. Now the depth of the ocean averages around three miles. The deepest known spot in the ocean is six and a half miles. So obviously 20000 leagues under the sea cannot be straight down. Such a distance would take you clear through the earth and way out on the other side.

Jules Verne wrote a wonderful yarn called Twenty Thousand Leagues Under The Sea. It is a story of an underwater boat written long before submarines were invented. The title  like the seven league boots of the fairy‑tales is somewhat poetic. Since it doesn’t mean 20 000 leagues straight down  then it must mean something else. And so it does. Captain Nemo took the Nautilus under water for miles and miles and miles. In his time he easily could have traveled through the ocean of the world for 20,000 leagues more or less.