Walkthrough guide

First, collect at least 4 fossils.

Next, rest at the tent and you will see a dream giving you a clue. To find these landmarks, equip the compass and follow the coordinates given in this guide. When you find the item to dig up from the clue, rest again to get the next clue.

Here are the landmark locations in order and the dig spot given by the 
landmark's clue note.

1. "A terrible beast... Emerges from the sand... North west..."
Landmark location: -40, -49
Dig spot: 63, 14

2. "To the north... Behind the visitors... Where bones rest..."
Landmark location: 41, -59
Dig spot: 18, 71

3. "A picture of the past... To the west... By the sands... Writ upon the rock..."
Landmark location: -67, 13
Dig spot: 06, 41

4: "An invitation... For a special day... West... On a platform of stone... Alongside a winding path..."
Landmark location: -24, 20
Dig spot: 12, 30

5: "Hidden between earth and stone... My burrow... North west... A path of sand..."
Landmark location: -60, -56
Dig spot: 50, 50

After you have discovered all the special finds, sleep again then go to the area where you found the burrow (-60, -64) and go through the hole to the mine.

Endings:

To get the bad ending, go to the end of the mine and wait for a minute, then the ending will play

To get the good ending, when you're in the mine, don't go to the end. Instead follow the paths marked by signs. The path with the triangle sign (it looks a bit like an arrow) leads to a clue to find a key. The path with the rectangular warning sign leads to a room with lockers. On the wall of this 
room is a poster and, as the clue in the other room suggests, if you dig in front of that poster you will find a key. This time instead of waiting after going to the end of the mine (you still need to watch the cutscene), retrace your steps and open the gate with the key you found. 
Congratulations! You got the good ending!