Royal tomb

Royal Tombs are where the remains of the past kings of Lucis lie in Final Fantasy XV. They are hidden around Eos in hard-to-reach areas and many legends surround their locations. Prince Noctis sets out on a quest to locate the Royal Tombs to collect the Royal Arms from their depths, crystalline weapons only the bloodline of the Lucian kings can wield.

Story
After Insomnia falls at the hands of the Niflheim Empire, the Marshal of the Crownsguard calls Prince Noctis and asks him to meet at the Royal Tomb on the Leide region. Noctis learns his father was killed in the invasion, and Cor explains Noctis must reclaim the royal arms from the tombs of the Lucian kings scattered around Eos, and helps Noctis get started on his mission by directing him to another tomb nearby. In the town of Lestallum Noctis and his friends learn of a legend of a tomb hidden behind a waterfall, and find another Royal Tomb in the depths of an ice cavern.

Trivia

 * There being thirteen tombs alludes to the game's origins as Final Fantasy Versus XIII. The originally envisioned Fabula Nova Crystallis: Final Fantasy XIII games had many references to the number 13.