Illusion Temple, Dispellado & Chrono Rune
Obtaining the Chrono Rune is an extremely easy process but extremely long. To start you'll need to completely repair the entire town of Adelhyde. You can start this side quest shortly after the town is destroyed very early on in the game but you can only do so much of it at a time. You won't be able to make the final donation until the end of the game.
It'll be about 10 donations in total with the final donation costing 100,000 Gella. After you make the final donation to the kid you'll want to check the Pub in Adelhyde for an NPC that wasn't there before, a Dream Chaser. You'll need to exit Adelhyde and re enter it after you make the final donation for this NPC to appear. He's in the northern end of the Pub, shown in my screen shot below.
Once you have the Dispellado in hand you'll want to travel to The Rings of Timespace which are just north of Baskar Village, you passed by them multiple times earlier in the game and probably even wondered what they were used for. If you're having trouble locating them, just use my map location below for guidance.
If you couldn't already guess, you'll need to use the Dispellado on each of the stones in a specific order which will grant you entry to the Illusion Temple. The order is shown in my screen shot below, click on it to enlarge it if you need to.