Added by Thaumcraft 2 mod
An Eldritch Monolith is a landmark that has a floating obelisk on the surface, 3x3 floor of eldritch stone. It goes all the way down to the bedrock and inside are some very interesting items like:
How to get in
Eldritch stone is very tough and cannot be destroyed even with a diamond or a Pickaxe Of The Core. One way getting in, (Atleast the one I know ~AwsmAssassin) is by using mining scroll. Raid some dungeons and find a mining scroll, which is basically a black coloured paper which when right clicked, mines any block. Take that paper in hand a right click in the middle block of the 3x3 floor. NOTE : Make sure to have a bird on your head so that you glide to the bottom and don't die of fall damage.
Another way to get in is to equip Goggles of Revealing. This will let you see some runes on the outside. You will then need some crystals. Red = Firey, Yellow = Vaporous, Green = Earthen, Blue = Aqueous, Purple = Vis, and Dark Purple = Tainted. For example, if I had a rune pattern that had 2 red, 1 dark purple, and 1 yellow, I would need 2 Firey crystals, 1 Tainted crystal, and 1 Vaporous crystal. Then take the crystals and put them in their respective places. NOTE: Misplacing a crystal will result in an explosion and the loss of the misplaced crystal. Nothing else will be damaged however. The middle block should disappear in a puff of smoke (which does not cause atmospheric Vis or Taint changes). Then simply climb down using Rope Arrows, Grappling Hooks, Ladders, Birds, etc.