The gilded cross is found as part of the Desert Treasure quest when looking for the Shadow diamond. It was stolen from Rasolo by a bandit named Laheeb. It must be stolen back from the Desert Bandit Camp where it is found in a very secure chest, which requires you to lockpick it three times in a row successfully in order to be opened. Once you have it, it may be traded with Rasolo for the Ring of visibility.
If you have a full inventory while you successfully pick all the locks, the cross will drop on the ground, and looting the chest a second time before picking up the cross will result in having two crosses.