I've just created a world for this achievement and you can find a link below.
All you need to do is...
Download the file from the link below.
To Import the World
1. From Main Menu --> Tools --> Scenario Editor. Once it's opened, click "File" (on the Top Left corner) then select "Load Scenario". (Click "NO" for saving the currently opened world because it's just a blank world, so click "no")
2. Now, Click "Open Saved Games" to open the folder that contains save files. Then Copy the downloaded file from the downloads folder to this(Folder that opened through AOE3) location.
3. Then close the File Explorer and back out from the Load Scenario to refresh that page. Open "Load Scenario" again and you can see the downloaded file appears on the list.
4. Now, you can open through "Scenario Editor" or from Main Menu --> Load --> Use Filter setting --> Custom Scenario --> "Save File" --> Open.
5. If you opened through the scenario editor, click scenario on the top bar, then select playtest scenario, make sure it selected as Player 1.
6. After loading the save, Wait for some time (look at the Minimap, Explorer will group up and looks like watching a cell merging through the microscope
) once they grouped together, select one group, attack a treasure guardian. meanwhile, select another group and start to attack the next guardians to pace up the progression. after killing guardians, Click again on the treasure to collect it.
Once you've collected 100 treasures, the achievement will pop!
Save File: https://drive.google.com/drive/folders/1FXZmB5Kk9Ogy2gLxqF8p...
You Can also find 3 other achievements save files inside the link.
Following Achievements are
If you have any issues with the file or any other questions, please comment below.