We have constructed a habitat for Withers in our upcoming update.
It a 115x115 cage which goes right down to bedrock and 32 blocks into the air.
Thanks Minerduck and Obsi for your great help with the construction.
Inside the cage is a swamp biome for Withers to blow up.
In our next update you will be able to fight Withers without damaging the rest of the map.
There are also plenty of skeletons and zombies in the cage to keep you busy.