If you are impatiently looking for treasures you shouldn't continuesly
drilling into the deep.
Be careful using bridges. Next to crossing rivers you can also jump
higher using them.
Don't waste your breath trying to drill through rocks. You better remove
them by using some heavy explosives. But be careful as water might get
into your passage.
Killing your enemies might remove them but it won't help you getting far
as the bank calculates in money not in dead bodies. Therefore you should
prefer digging for treasures instead.
Make sure you save the game every time after finishing a zone.
Sell your treasures immediately to avoid it getting stolen.