At the end of Route 3, you find the entrance to Galar Mine.
Explore Galar Mine
The pokémon that you may see in this area are Carkol, Diglett, Drilbur, Roggenrola, Rolycoly, Timburr, and Woobat.
Go north and check on the sparkle to the left of the mine cart to get a Star Piece.
Then go west and follow the tracks. To the left of the tracks, check on the sparkle in front of one of the mine carts to get a Revive.
To the left of that, you can battle Worker Keith, who has a level 14 Roggenrola. You get 1400 Pokédollars for winning.
If you go west from there, you will see an item to the right. Keep going south, then go north up the northeast path to reach the item: 3 Great Balls.
If you go south from there, you reach a ledge outside where you find TM54 Rock Blast.
Go north to re-enter the mine, take the northwest path, and keep going north past Worker Keith. If you go south on the tracks, you can encounter a wild Carkol.
Go north along the tracks and you can go west to battle Worker Georgia, who has three level 14 Timburrs. You get 1400 Pokédollars for winning.
West of Georgia, check on the sparkle to the left of some crates to find a bag of Stardust.
West of that, you find TM26 Scary Face.
Go east past Georgia, and go east along the tracks. From the end of the tracks, go north and check on the sparkle near the east wall to get a Hard Stone.
Go north and you will battle Worker Sandra, who has a level 14 Diglett and a level 15 Drilbur. You get 1500 Pokédollars for winning.
Go north across the bridge. Northwest of the bridge, there is a sparkle in front of some crates. Check on it to get an Ether.
East of that, you can battle Worker Russel, who has a level 15 Rolycoly. You get 1500 Pokédollars for winning.
East of Russel, there is a pair of Heavy-Duty Boots.
North of Russel, check on the sparkle near the wheelbarrow to find a Revive.
Go west and follow the tracks. To the left of the tracks, you will find 2 Super Potions.
Go north and there will be a cutscene. If you are ready for a battle, go north and you will battle Pokémon Trainer Bede, who has a level 13 Solosis, a level 15 Gothita, and a level 16 Hatenna. You get 1920 Pokédollars for winning.
There is a tunnel to the north, and there is a sparkle to the left of it. Check on the sparkle to get a bag of Stardust.
Then go north to leave the mine. You will arrive in Route 4.