It's Viggo's upcoming movie which he will start filming soon! There's an address for it available there, make sure to check it out! 
And I agree with you, Fanmail.biz is the best fan mail site online, people should rather use this site than any other site!! 
Good luck to you, Chris! Viggo is a pretty good signer via venue... At the end, it always depends if the venue/movie studio passes on the mail to him, so you might want to check if the studio has a good reputation when it comes to fan mail!
Regards,
Lizanne