The ring of visibility can be obtained from Rasolo the merchant, after the player retrieved his cross for him during the quest Desert Treasure. Wearing the ring lets the player see certain ghosts and items that are normally invisible. The ring of visibility cannot be made using the Crafting skill.
When all tracks in May's Quest Caravan have been completed, the ring of visibility will gain the ability to hide you from monsters untill you attack them. Note: this does not include bosses like Giant Mole orZilyana
It used to be possible to obtain multiple rings by using the drop trick.
The ring is described to let the player "see into the shadows", a possible reference to the One Ring from The Lord of the Rings.
During the quest Fate of the Gods, it's hinted that Sliske is the creator, or perhaps a previous owner, of the ring of visibility as he says, "Ah, I see you are wearing that little ring of mine" when the player is wearing it to see the World Gate.