This Fortnite challenge should be relatively simple, as there are multiple artefacts in each location.
Here's where you can find them.
Where to find artefacts at Stealthy Stronghold
The artefacts at Stealthy Stronghold resemble statues of prehistoric reptiles.
The two artefacts we recommend aiming for are in the ruins in the eastern section of Stealthy Stronghold.
Where to find artefacts at Coral Castle
The artefacts at Coral Castle are solid gold, and represent Fishsticks' ancestors!
The artefacts found at Coral Castle are quite showy. The easiest to find is at the top of the small sand dune to the east.
The second is well hidden -- embedded below the surface, just below a stone arch.
The only real difficulty with this challenge is the presence of other players seeking to complete the same task. Be sure to arm up before you head to the location, so you can defend yourself!