Wither Alter

This structure is a part of my larger idea to add a biome to the nether called Withered Nether:

https://feedback.minecraft.net/hc/en-us/community/posts/360048333892--Nether-Biome-Withered-Nether

The Wither Alter

This is a structure found in the Nether (hopefully Withered Nether) where the wither would be summoned. Physically, it is a platform that would sit high up on a tall tower in the middle of a large open space, and it would be composed of Wither Alter Blocks. Alter blocks would be indestructible, like the End portal frame. Spawning the Wither would still require the same skulls and soul sand in the same structure, but those blocks would have to be sitting on top of a Wither Alter Block for summoning to occur. 

This structure is necessary because currently players can pick the environment they fight the wither in, thus largely removing the challenge the fight is supposed to be. Underground wither fights are a common strategy because the tight space limits where the wither can go. Some players use the bedrock under the central End portal to reduce the fight to a grind. But where the Wither really shines is in a more open area where it can fly around up high.

It is important that the Wither fight be somewhat difficult because Nether Stars are supposed to be very valuable and hard to obtain - it's why the wither exists in the first place.