goldendragon1597, on 17 August 2012 - 12:26 AM, said:
That is a feature in the mod Thaumcraft 2. To open it equip goggles of revealing. You will see symbols on the bottom of the obelisk. Place the crystal shards (forgot what there called) on top of there symbol (judge by color). For instance, you should see a yellow symbol, so place a yellow crystal on it. These crystals can be found in caves. They emit light. After it has been opened, carefully make your way down. There should be some valuable treasure inside. Research it!
The items inside the obelisk, known as the 'Eldritch Monolith,' allow you to research Eldritch knowledge. Of course though, if you do not know much about Yogbox, this will mean absolutely nothing to you, but many good things can only be obtained with eldritch knowledge. Look it up and you should find a bunch of items that need it.