Castle to chateau doesn’t have its own sign up. You just have to sign up for a half in the states and a half in Paris. I don’t recall when bib only typically opens up. There are other Paris threads here that have more info on that.Ok. Do you know when they typically open? The usual cost? Is there a way to sign up for castle to chateau? I found a great price on plane tickets, but don't want to book those unless I know I can get into the run.