Tactics Ogre: Reborn has a wealth of late-game content to explore, and the Ancient Temples, also known as Elemental Shrines, are one of the best examples, with great loot available in a set of unique and atmospheric locations.
Unlocking the shrines is not an easy task, but this guide will show you every step along the way.
Fortress & Shrine Locations
Each of the Shrines has a Fortress that must be beaten first to reveal it. Below is a complete list of all the locations, so you can check what you have completed, and above you can see their locations on the World Map.
Read The Talk Topics
The most essential step in unlocking the Temples is to complete the story battle at Barnicia castle and then watch the cutscene that follows at Phidoch Castle. Once this is complete, a new Talk Topic will appear called The Ancient Temples. Once you have read this, a number of the overworld fortresses mentioned above will reappear on the map, and others that were already visible will have battles enabled. These locations will not show the usual red color indicating an unfinished battle, but when you go to the fortress, it will trigger.
Unlock The Hidden Fortresses
Two of the Fortresses that need to be cleared also require completion of other Talk Topics and Story quests to get them to appear on the map.
This fortress will only appear once the "Mysterious Blast on Exeter" Talk Topic has been read, and the battles at Madura Drift, Belmorose Highwilds, and Vasque have been completed. Once the Vasque battle is complete, Lhazan Fortress will appear on the map. However, you must first complete the Occione storyline quest (you do not need to recruit her, only finish the battle in Lhazan Fortress up to the point at which she joins or leaves).
Once this step is complete, you must leave Lhazan and read a further Talk Topic "Galgastani sighted at Lhazan," and you will then need to return to the Fortress to trigger a further battle.
This fortress will only appear once the "Rhamsen Wreck Raised" Talk Topic has been read and the battles at Leupha Coast and Grimsby have been successfully completed.
Complete The Initial Fortress Battles
At each of the six fortresses, a battle must be won against the current inhabitants. You will face a variety of foes, from Pirates, to Rebels, and even the Undead. Mostly this will also mean fighting uphill against enemies at higher elevations and with ranged attackers who make the battles tough tests of attrition.
Each battle will require you to defeat a single leader, so if you have flying units or ranged attackers who can target them from afar, you can win these quite quickly by focusing the leader down. Otherwise, prepare for a long slog and bring lots of healing.
Unseal The Shrines
Once all the fortress battles have been won, you should head to Coritanae Keep. A cutscene will trigger with a conversation with Archiereus Mreuva, at the end of which you must respond to his question.
Select "I know I will" and he will reveal the secrets of the Shrines and the magic held within. Once this custscene is complete, you will have two new Talk Topics "Dorgalua's Great War" and "The Apocrypha."
Read these, and then return to any of the fortresses while you have any of the four Phaorena sisters (Cerya, Cistina, Olivya, and Sherri) in your roster, and another cutscene will trigger in which they open the temple below.
You can now explore each of the Shrines and grab the rewards within.