Play through and beat the game once then you'll start and new game with achievement mode unlocked which give you these shelves in your garage, now you can start hunting.
And once all is collected you get golden tools.

Once you dig down to -100m you'll find a mine, just follow the path and at the end you can grab the treasure. Congratulations, you've beaten the game!
Pretty straight forward, just keep digging with the shovel and eventually you'll get it.
There's a crate in your garage that needs two keys to be unlocked. These keys can be found underground and they don't seem to have a set location, so it's different for everyone. But I found mine at -20m and -39m so check around that depth and you might find them.
You need to dig a wide enough hole so you don't hit any walls all the way to the bottom and jump in from the top until you hit the ground.
Dynamite is available at the shop for 100$, throw 100 of them in total.
Rainbow ore can rarely be found underground at any depth, they aren't used for anything other than this achievement.
Once you start collecting platinum and diamond at a deeper level you'll earn that money in no time.
Head up to the surface and start collecting stones.
Fill up your inventory and head up to the surface. Start digging up all of the stones and a message should popup for each one that says "ORE DESTROYED".
To beat the game under 30 minutes you need to be moving around fast.
Focus on shovel upgrades but don't forget about the others.
Try to avoid digging horizontally and only go straight down in a narrow hole.