First you talk to his wife to get quest

Then you go to the coast and see the boot on the ground see screenshot


Then return to Alba and come back to coast again

You will need 3 Runes Blue, Green and Red
You will also need 2 circular and 2 triangular stones










By assembling the 2 circular stones and 2 triangular stones, you will open a secret passage where you will can assemble the 3 ruins and get the unique armor. Additionally, there is a lock to be picked and a treasure to be found (Yielding more achievements)

You will need to do side-quests to get this:
You have to do Alba's quest and the golden armor. Upon getting these, you should get a fame of over 300


If you are still below 300, go back to the island where pirates are stuck and buy the necessary gear for them. This will give you an additional +5 fame.

New according to MelmQuty in the comments: "After the finish of the game you can earn +5 fame. You need to visit the first location of the game(village),where you will talk to your brother and sister, after it you visit Hobston(a man who lives alone on the island).The last part is to visit the place where we fought our brother before and help Hobston."

"After the finish of the game you can earn +5 fame. You need to visit the first location of the game(village),where you will talk to your brother and sister, after it you visit Hobston(a man who lives alone on the island).The last part is to visit the place where we fought our brother before and help Hobston."