If you click the sword, it reveals this secret:
What a fine sword you’ve found! Its craftmanship marks this as a royal weapon: this is a sword belonging to one of the Lost Lords of Narnia. Ther are seven swords in total, one for each Lost Lord… Can you find them all? It’s a challenging task, but well worth the effort if you can see it through.
Looks like the challenge is going to begin here at Narrowhaven and spread throughout the rest of the islands.