Japanese state guesthouse was build as "Akasaka detached palace" in 1909.
This is the only neo-baroque architecture in Japan.

http://upload.wikimedia.org/wikipedia/commons/6/6c/State_Guest-House_Akasaka_Palace%2C_Main_Yard-2.JPG

http://upload.wikimedia.org/wikipedia/commons/b/bd/State_Guest-House_Akasaka_Palace.JPG

http://www8.cao.go.jp/geihinkan/images/gei1.jpg

http://www8.cao.go.jp/geihinkan/images/gei2.jpg

http://www8.cao.go.jp/geihinkan/images/gei4.jpg

http://www8.cao.go.jp/geihinkan/images/gei5.jpg

http://www8.cao.go.jp/geihinkan/images/gei8.jpg

http://www8.cao.go.jp/geihinkan/images/gei9.jpg

I walked by this beauty almost every day for 4 years while attending Jouchi!

Japanese state guesthouse was build as "Akasaka detached palace" in 1909.
This is the only neo-baroque architecture in Japan.

http://www8.cao.go.jp/geihinkan/images/gei2.jpg



State Guest House Annex is to be built by the year of 2009 next to the palace.
Annex is the house in Japanese style and was designed by Tadao Ando and Ken Yasui.

So it's a state guest house now... what was it used for before? Was it once the home of the royal family?

Yes, it used to be the palace for the Prince Imperial.
Now only nation's guest (stricltly, only the head of state of a foreign country) is allowed to stay by Imperial Household Law.