LOL!!!
Okay - Leprechaun's treasure - you need to go into Anephas' Tomb/Temple of Isis, Sphynx outside the front door. Way down inside there is a place where you will gain access to see Kerah. When you do - you can swim out from her little underwater niche and when you reach dry land, you will find the chest in question. When you open it, the Leprechaun will appear and blah blah blah at you. Inside the chest is the item you need to fulfill the quest!
Wyv