CryshalTirith

Cryshal-Tirith is a crystalline tower created in the image of, and by the Crystal Shard, Crenshinibon. It exists wherever the Shard is, can replicate itself, but it grows less powerful with each copy. The tower itself absorbed the sun's light, giving it more strength during the daytime. The tower was impervious; it absorbed all attacks against its mirrored walls and reflected them back on their source. The only vulnerable part of the tower was its heart, the pulsating crystal of strength that was used to construct the tower, and that became hidden away within Cryshal-Tirith. The tower's very door was invisible and undetectable to any beings inherent to the present plane the tower rested upon.