Go to the Wiki link that Gamemaster provided above for you.
From there you can click on the different story names provided there.
There are some fantastic vintage stories that are still currently on sale for 100 gems.
There are also some other stories available for 500 gems.
Once you buy a story you will have 28 days to complete it.
A lot of the stories available to purchase have repeatable mines & recipes.
Once you click on a story name you will go to another Wiki page dedicated to that particular story.
That Wiki page will give you in depth information in relation to that particular story such as camp equipment, names of the story/repeatable mines, how much energy is required to clear each mine, what treasure, achievements, experience, coins, materials, food, gems, precious stones, energy/gods children & special items can be gained.
A few stories even give camp equipment for free as a final reward.
I've just taken a screenshot from The Magisterium to give you an idea of how to understand the camp equipment table.
The column with the red square above it is the regeneration camp equipment.
The column with the pink square above it is the capacity camp equipment.
The column with the green square above it is the game level required to be able to acquire that piece of camp equipment.
Hopefully this gives you some more insight.
On another note twice a year Pixel has a Grid Unlock Discount week which reduces the amount of materials needed to dig out your underground camp slots by 25%. The last one was on 26 May to 2 June 2020. So the next one should be due reasonably soon. It's a good idea to try to stockpile as much materials as possible before then.
This Wiki link gives you details of how much & what type of materials are needed to unlock the entire underground camp slots.