The Beacon Tower (also known as the Spawn Tower, which you see once you spawn, hence the name) is the large tower in CastleMiner Z made up of bedrock and lanterns. You spawn approximately 32 meters from it's base of varying altitudes. It consists of a 9 block diameter at it's thickest point. From there, it slowly decreases to a 7 block radius and 5 block radius. But once it reaches the 3 and 1 block radii, lanterns begin to coat the top of the 6 block layer (the lanterns are actually the 7th layer).
(Borrowed from the CastleMiner Z wikia)