Where do I find all the artifacts?

There's more on worm tiles

• a worm tile's drop is the same drop per day every time you reload the game
• some worm tiles don't despawn the next day

With these two elements, all you have to do is

• wake up
• look for these worm tiles and dig them
• if you haven't found anything interesting, just reload the game and redo your day as normal
• the next day, wake up and repeat the first steps

The problem is that some artifacts are very rare and this method will work hardly on seasons other than winter. The solution (yes it's cheating) is to change your save game file to put more worm tiles in a zone!

• BACKUP YOUR SAVE GAME FILE (%appdata%/stardewvalley) This is very important because when you close the game it might upload a corrupted filegame in the steam cloud!
• go to the beach and look for an artifact spot, it must be surrounded by sand (no rocks, shells,...)

• open your save file and search for "beach", it must be in a <gamelocation> xml tag

  <GameLocation xsi:type="Beach">
  

• slowly search further for "Artifact spot", once you have one, copy somewhere else all the text including the <item> tags

  <item>
      <key>
          <Vector2>
              <X>38</X><Y>10</Y>
          </Vector2>
      </key>
      <value>
          <Object>
              <specialVariable>0</specialVariable>
              <category>0</category>
              <specialItem>false</specialItem>
              <hasBeenInInventory>false</hasBeenInInventory>
              <Name>Artifact Spot</Name>
              <Stack>1</Stack>
              <tileLocation>
                  <X>38</X><Y>10</Y>
              </tileLocation>
              <parentSheetIndex>590</parentSheetIndex>
              <owner>0</owner>
              <name>Artifact Spot</name>
              <type>asdf</type>
              <canBeSetDown>true</canBeSetDown>
              <canBeGrabbed>true</canBeGrabbed>
              <isHoedirt>false</isHoedirt>
              <isSpawnedObject>false</isSpawnedObject>
              <questItem>false</questItem>
              <isOn>true</isOn>
              <fragility>0</fragility>
              <price>0</price>
              <edibility>-300</edibility>
              <stack>1</stack>
              <quality>0</quality>
              <bigCraftable>false</bigCraftable>
              <setOutdoors>false</setOutdoors>
              <setIndoors>false</setIndoors>
              <readyForHarvest>false</readyForHarvest>
              <showNextIndex>false</showNextIndex>
              <flipped>true</flipped>
              <hasBeenPickedUpByFarmer>false</hasBeenPickedUpByFarmer>
              <isRecipe>false</isRecipe>
              <isLamp>false</isLamp>
              <minutesUntilReady>0</minutesUntilReady>
              <boundingBox>
                  <X>2432</X><Y>640</Y>
                  <Width>64</Width>
                  <Height>64</Height>
                  <Location>
                      <X>2432</X><Y>640</Y>
                  </Location>
              </boundingBox>
              <scale>
                  <X>0</X><Y>0</Y>
              </scale>
          </Object>
      </value>
  </item>
  

• you can now duplicate this item block by changing the X Y coordinates near the initial worm tile. For the values of the bounding box you must do a simple division (in my case, 640 / 10 => 64) to find this number and adapt it to new coordinates

• put the new item blocks next to the one you found in the save game (that you have backuped of course)
• load the game
• dig
• ????
• ARTIFACTS!!