From the Super Mario Wiki
Klepto Ruins is one of the places in Mario Party Advance. It is located in the Desert Area of Shroom City, but it can only be accessed by a pathway at the entrance to the Seaside Area. When the player decides to stop here, he or she meets Mr. E, who is confronting Klepto about a secret treasure. His quest, Treasure of Mystery!, involves opening Klepto's treasure chest by guessing the correct four-number combination. If the player gets it right, Mr. E will be fascinated, though he quickly loses interest and leaves, leaving Klepto to reward the player with the Map Maker Gaddget.