This page explains how to find the Ritaag Zumo shrine.
How to Find the Shrine
Go to the ruins that are at the southern end of the spiral. There you will find a glowing orb. Carry the orb along the spiral until you reach the center. You can also throw the orb into the water and use Cryonis under it if you want to avoid some of the enemies.
At the center of Rist Peninsula, put the glowing orb into the pedestal to make the shrine appear.
About the Shrine
The chest in the shrine contains a Giant Ancient Core.