[asploder]

What exactly would a Mars colony need to dig tunnels for?

[Matt3o12_]

According to many experts, this would be an easy way to shield humans from the radiation. A glass dome could also work but would be more expensive and could be fragile.

On the other hands, tunnels do not provide any sunlight but I don't know if humans can actually use the sunlight on Mars (so a dome might be necessary as an addition or completely irrelevant anyways).

[gaius]

Protection. Meteorites not burnt in the sparse atmosphere. Thermal stability. Radiation.

[probably_wrong]

The article mentions that communicating Mars houses with tunnels might be the best way to deal with the loss of breathable air.