This castle is somewhere near Franklin, New Hampsire; it came up while digging through long defunct Geocities sites. These folks are truly building a DIY castle out of local materials one stone at a time. One of the pages is titled "How to build a fieldstone castle, cheap." The tower in the picture apparently only cost $2000. The site has a crazy layout and it's not the easiest to get around, but there's some interesting information there. I've sent an email in hopes that I can get more information about the castle and how it was built to share here. I'll post more if it happens.
EDIT: After returning and checking the site out more, I don't think the resulting room is anywhere near castle-like. I'll leave the post here all the same as the site shows how to build with stone and cement cheaply, which is still useful and interesting.
