system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are underwater tunnels built?

Seriously HOW? Underwater tunnels are the one thing that convince me we are living in a simulation. It seems impossible to build one. And they always look so perfect. HOW?
gpt
Some tunnels are drained before the drilling.

You can also use explosives to blow a hole and then use rocks/bricks to make everything look nice

You can also use pressure cannons to tunnel through things under water.

Is there a specific tunnel that you're trying to figure out?