science fiction book, perhaps mid-1980s or even earlier

I owned this book as a used paperback in the mid-1980s.
It was the story of a young man who believes his super-wealthy grandfather(or father, or godfather, I forget) has basically disinherited him, because out of the entire estate all he is bequeathed is the old man's family home.
He discovers, though, that the house itself is some kind of portal to other worlds.
Or perhaps it actually creates those other worlds, as part of a huge computer virtual reality.
(Which the book was very early in positing.)
The young man is seen by the computer, and by those inhabitants of the realities he encounters, as the heir of his omnipotent father-figure, and the riches and power this supplies far out-weighs the estate in the mundane world that bypassed him.
He enters into a virtual world, where he is accompanied by a female guide created by the computer to assist him.
There are various adventures, including traveling by glider.
The actual reality of the worlds, and the girl, remains a bit unclear.
Help?