A legendary treasure map is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of Legendary Treasure Map in Evony TKR says:
Use it to locate a Lv4 Relic to search for Treasures.
Legendary Treasure Map is known to drop from a number of bosses or monsters upon killing, including Peryton, Minotaur and Royal Thief.
Note: This list may be incomplete.