How deep is 520 leagues?
It's about 1,500,000,000,000 times as long as a Mitochondrion
The length of a Mitochondrion is about 0.0000000003380 leagues.
(Eukaryotic; average)
A mitochondrion measures between 0.75 and 3 micrometers (µm). The mitochondrion is commonly referred to as the powerhouse of the cell, responsible for the generation of ATP. The size, shape, and distribution of mitochondria varies widely, with human liver cells each having 1,000 to 2,000 mitochondria.
It's about 2,000,000,000,000,000 times as wide as a Glucose Molecule
The width of a Glucose Molecule is about 0.000000000000270 leagues.
(C6H12O6, a.k.a. grape sugar) (open chain form)