Sassy McSassafrass said
Everyone knew the Stone Tower was built upon a tear between the realm of the living and the dead. It was built to contain and control that tear. The doors of the tower were sealed to prevent it being flooded with the dead returned to life. That was the popular legend but it was also said that the Tower was what created the tear in the first place.
Gosh, Alex has been hearing a lot of very strange things. I don't know what all this tear between realms business is but perhaps I can elucidate this a little bit for our purposes because the game is vague on what went down. In this canon, no one actually knows when or why the Stone Tower was built, but it's widely known that the Ikana most certainly didn't build it. Following a very costly war with the Garo Ninja that involved a siege of this mysterious stone tower, the kingdom of Ikana fell into ruin after being completely ravaged by the war, but not before the last of the Ikana sealed the doors to the tower to contain all the restless vengeful souls that remained within.
30 years ago, the Skull Kid comes along and breaks the seal on the tower, which causes the lingering spirits within the tower (like the Garo Robes and the Stal Knights) to begin plaguing Ikana again. Dampe the Oathkeeper climbs the stone tower and defeats twinmold, resealing the temple and laying the spirits to rest once again. Present day, some dark magic weakened the seal, which led to war with this undead legion.
Does that all make sense? The Stone Tower doesn't contain a portal to the realm of the undead, it just houses lingering vengeful spirits that perished during that bloody war between the Ikana and the Garo. S'all gravy though.