Japanese Art Dealers

I have a label of a package that was sent to me said Nakazawa, Opp. The Imperial Hotel, Tokyo, Japan 591-2553. I would like to find the exact address of this place to post something for them, but this seems like a partial address. I think the OPP. ways in front of the Hotel Imperial. I tried Google and some stuff came but it was not useful, because I do not speak or read Japanese. I think Mr. Nakazawa is the name of an art dealer. Ideas?

81-3-3591-2553 is the telephone number of the art gallery called Gallery rental Hibiya, 6-5, 1-Cho-me Yuraku-cho, Chiyoda-Ku, Tokyo, just behind the Imperial Hotel Tokyo but I do not think Mr. Nakazawa is housed at the art gallery rental.

I do not even know if it as below is actually the person you have spoken so.

http://nmpainting.nmdo.net/index.html

Tokyo has the zip code '591-2553 '.
59x-xxxx is in Osaka.
But the address is Imperial Hotel Osaka
0.8 to 50, 1-chome Temmabashi, Kita-ku, Osaka 530-0042, Japan
I assume that the address is not based on fact.
so I do not know what "Opp" means.