Talking to the people in the houses yield no results on what it really is.
In simple terms... you can't. That house was originally where E-reader battles would take place, in the room/garden/whatever it was supposed to be in back. Ruby and Sapphire were compatable with the E-reader, but Fire Red, leaf Green, and Emerald are not for some reason. (NOt knowing much about Nintendo, I'd say that the E-Reader died out before the games came out, and was thusly replaced with the Wireless connector.) However, for some reason, the house remains in both the Kanto remakes as well as Emerald.
You can only go into the house in Japanese versions of FR/LG and RSE.
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