I dont know about many others, but I myself and a couple of friends love to build under water!
It would be an amazing idea if there was a some form of item or useable that drains a totaly insulated build of water !! The possibilities would be great!!
And glass… we have glass. Can make glass orbs and such. But we cant make windows? Of any kind… I mean heck the option to create dyed windows should be there ! But even any kind would be amazing.
An aquilonian underwater mansion with glass windows? Come on!!