To go to Crespo Island Forest, you should wear something similar to a modern diving suit, such as a copper spherical helmet, a metal compression suit with an oxygen bottle behind it (the book says that you can breathe underwater for several hours), a pair of lead shoes, which are too heavy to move on the ground, and a rifle that fires charged glass balls with compressed air. Ni didn't go

Because he heard that he was going to sink to the bottom of the sea and could not carry out the escape plan.