Well now you do!
Thanks to the latest GE update, you can use the flight simulator underwater.
This is what the Marianas Trench looks like from the cockpit.
That's about as deep as you can get. Some bloke called Piccard went down there in a sort of submarine about 50 years ago. The deepest part of it is called the Challenger Deep and it's about 35,000 feet below sea level. Even there, at incredible pressure, life exists.