http://rzuwtpc4wb3xdzrj3yeajsvm3fkq4vbeubm2tdxaqruzzzgs5dwemlad.onion
If you sign in to that website, they still don't know your location but they know who you are.
Further, if you provide: name, email, address, phone number, or any other personal information, you are no longer anonymous to that website.
The best defense is to be vigilant and extremely cautious when filling out web forms.