The Wolf House is a place where Roman demigods start their demigod life. It is there where Lupa judges whether the demigods left there are worthy and strong enough to endure her training. If so, she adopts them as her cubs, as long ago she adopted Romulus and Remus, teaching and conditioning them until she judges them worthy of taking their place as Legionaries of Rome. Then she gives them directions to Camp Jupiter leaving them to fight their way there alone; conquer or die.
The Wolf House was built by Jack London (writer of Call of the Wild, White Fang etc), a son of Mercury. It is where he found out he was a demigod. London thought that he could live in it, but it burned in a fire a week before he and his wife were supposed to be moved in. A few years after this event he died and his ashes are buried on the site.
Hera, Queen of the Gods, gave Jason Grace, son of Jupiter, over to a she-wolf named Lupa in the Wolf House. Years later, Jason is reunited with his sister Thalia Grace and they find Hera trapped in the house. Leo Valdez and Piper McLean work together to free Hera while Jason fights Porphyrion (who rose up from the house's pool), a giant born to destroy the gods. After Hera was freed and unleashed her true form (and almost killed Jason), Porphyrion escaped, the monsters died, and the hunters unfroze.
The land itself is said to be a site with tremendous power, which was the reason that Hera was trapped at this location and the reason Roman demigods start their journey here. Khione's plan was to kill Jason at the Wolf House so that his blood would curse the land and give Gaea enough energy to wake. The plan failed however when Leo fought off Khione and Porphyrion retreated after Hera was freed from her cage.
The Wolf House and Lupa are mentioned several times by Percy, and it describes that earlier in the book he wakes up there. No memories, just Lupa. He had to start off his journey when the wolf goddess felt he was ready, and from then on the Wolf House is not mentioned. If so- then very subtly.
It was described in The Lost Hero as looking like what a millionaire lumberjack would build.