What runes are needed for?
Runes, 6 in total, are needed to add two magic combos to Ianna sword. These attacks will be very helpful in further levels because of their high damage and long range.
Defeating Dal Gurak boss without Ianna sword will be extra hard, as he prefers to teleport away when you come close to him.
Also, these runes are needed to descend into the Abyss - final level of the game with Chaos Child boss.
How to find runes?
Finding all 6 runes by yourself won't be easy during initial walkthrough. Sometimes you have to press a little button or, even worse, shot it with an arrow. It's hard to notice these marks because of the vast level area and enemies distracting you from exploration.
It gets much better after you get the Ianna sword. Old locations will open again for rune search on a world map, and completing them, you won't need to look for keys or face hoards of enemies.
The only 3 types of enemies you face now are fire-breathing demons, vampires and a Chaos Knight. Unless you want experience for your hero, none of them are needed to kill. They also help you in a search: Spawn demon, the weakest monsters, start chasing you if you move in a right direction. Vampires will start to attack you when you come closer to a secret button. The final mob, Chaos Knight, always appear from a thin air near a ruin. Pay attention to environment, and you should find something suspicious.
If you don't have time to search runes on your own, then continue to read this article to see exact coordinates.
Fortress of Tell-Halaf
The first rune is the easiest to locate. Just run forward in a straight line till you see Chaos Knight. Jump down and enter a corridor behind a waterfall. Run a dozen steps ahead and on the right side of the wall you will notice a button with a ruin sigh to open a secret passage.
Mines of Kelbegen
If you manage to recall the Green Gem location, the half of the work is done - a secret door is very close to it. The trap that await you requires you some climbing skills.
Tombs of Ephyra
Find a room with a big tomb and look above to see a button. Shoot it with an arrow to open a door.
Be aware that there is a very nasty trap in one of the narrow corridors ahead.
Oasis of Nejeb
Remember a temple with 6 moving columns? Enter if, but don't come down from a second floor. At the end of it, you will find another secret button to shoot.
Prepare your bow to shoot 4 targets as fast as possible to avoid death by lightning in the challenge ahead.
Fortress of Nemrut
After you entered the Temple and face a Knight of Chaos, go up the stair and then look back. The button you will see will be the biggest of all.
Temple of Al Farum
This rune is very far from the start of the level. It's close to the golem that appeared during initial walkthrough.
If you got confuses, watching a video guide should make things clear.
All runes video guide
The video contains full route to all runes without any fighting with mobs.