Although I haven't (yet) had a response from Plymouth,my "Googling" has discovered this:~
.Walking past the blue railings here, look for a famous order given by Sir John Hawkins to his fleet off Spain in 1564
This is from an official Devon.Gov site.
If you look at this picture you can see why it's known as an optical illusion.I think you can only see it complete if you view it straight on?
http://www.bbc.co.uk/..._walk_gallery.shtml?9
If the Ferry Terminal lets me know anything different I will post it.