Here is a huge/difficult island with only 55K that has tons of tunnels: https://maps.app.goo.gl/abcnXtRNs9QdVkhC8 https://maps.app.goo.gl/abcnXtRNs9QdVkhC8 Pop

Here is a huge/difficult island with only 55K that has tons of tunnels: https://maps.app.goo.gl/abcnXtRNs9QdVkhC8 https://maps.app.goo.gl/abcnXtRNs9QdVkhC8 Population size, density, terrain, etc. have nothing to do with it.