Somewhere in the south-east of Ardyl, you will find a very suspicious looking Antique Dealer, Drakus, who will tell you how the Sun Cross was stolen by the Priests of Kaliba, and ask you to recover it for him.
On level 3, you will come across a Monastery devoted to the goddess Kaliba, but only disciples of Kaliba may enter. Continue to level 4, where you will find Gondoor, he will tell you to enter this room, and find a key. Once you have chosen the correct lever, and found the key, use it to enter the next room, where Gondoor will say you must kill the prisoner in order to escape, however, if you venture past the prisoner a little, you will find another lever, which will release 2 spiders, one carrying a key that just happens to fit into the door. Enter the next room and you will be told you have made a wise choice.
Talk to Gondoor and you will be given an amulet and the choice of 3 swords of varying quality... may I suggest the one closest to Gondoor? Once you have picked your weapon, return to the Monastery, but before you enter, search the body laying on one side of the Monastery and you will find a scroll telling of a secret passage, then proceed to enter while wearing the amulet you received from Gondoor. Now in the Monastery you will find a cross on a table, however don't touch this one, and remember the scroll telling of the secret passage? Check the walls around the entrance, and you will find a torch, click on it and the bookcase next to it will move to reveal a passage. Proceed down the passage and you will come to a coffin, open it, but be ready for a fight. Once you have killed the skeleton and retrieved the Sun Cross, return it to the Antique Dealer.
Once you have handed it over, he shows his gratitude for you stealing the Sun Cross for him, and how happy Draak will be, then Drakus and his assistances will turn into monsters and attack you. Kill them, and the spectre, or Drakus if you like, will drop the Crystal of Wisdom.