the guestbook can be found by clicking the book gif on the site index page.
if you are having trouble accessing the guestbook, please try disabling automatic redirects to HTTPS in your browser. this setting is called different things in different browsers, so just search it up for your own browser.
note that this setting seems to have issues working properly in firefox in particular (may continue to redirect you even if it is disabled). double clicking the link on the error page may work, or you can try using a different browser temporarily.