Snow Castles are large pre-built castles added by Better Dungeons which primarily generate in snowy biomes (being Ice Plains, Alpine, Glacier, Ice Wasteland, Tundra) that contain Walker mobs. As with all Better Dungeons structures, these contain a number of hidden rooms and passages, making the need to thoroughly check these castles greater.
The names of these castles are taken from the files where their information is stored.