Can you build with packed ice? And if so How? How about lighting, won't torches melt it? I have this survival challenge going, but found this. If this isn't asking for a castle built out of ice I don't know what is.
That tower is 3 blocks by 3 blocks, which would be fine to hollow out for a ladder. Anybody care to guess how tall? I have no idea, but it is up there. Then expand the top a little for a room or two. Turn those ice spikes around it into castle walls, preserving the ice spike look of course.
Will mobs spawn on packed ice? I'm on 1.7.2 so things may have changed. I kinda like the idea of limited lighting, ice is pretty bright in the moonlight anyway.