The Blaggi Tower is a gigantic tower that is stationed on the far-western point of an island north of Agustria in Fire Emblem: Genealogy of the Holy War, and it is mentioned in Sleuf's ending in Fire Emblem: Thracia 776. In Genealogy of the Holy War, Claud, accompanied by Tailto, visits it in Chapter 3 to find the truth of Prince Kurth's death by praying to Blaggi, and to obtain the Valkyrie Staff. Claud finds out here that Duke Reptor and Duke Langobalt were behind the Isaachian-Grannvaleian War as well as the death of Prince Kurth, but his visions also found out that something else was behind this, but this something couldn't be discerned. Also, if Dew visits the Blaggi Tower, he will obtain the Wind Sword.
The purpose of the Blaggi Tower actually is very surprising. Saint Maira, who is the brother of one of the Emperor Galles started a rebellion that was supposed to help the people, but it failed. However, people who followed Maira lived on, and one of these people was the Crusader Blaggi, who before he was a Crusader, was a holy worker who received the teachings of Maira, and he was about to become a sacrifice to the Dark God, but another bishop who followed Maira saved him, and then Blaggi grew up on an island located north of Agustria. After Blaggi became a Crusader and the Empire was destroyed, he came back to the same island he grew up on, and decided to build the Blaggi Tower here. One theory states the tower was built as a place where his powers could be sealed, but its real purpose was to mourn for the priests that had followed Maira that had died to save the world from destruction, and to tell the world that there actually were people in the Imperial inner circle and the Lopto Sect that saved the people, at the cost of their own lives.