It's only 1,800 square feet, but architect Robert Venturi packed a lot into this house. Particularly, a lot of light.

"I've asked myself, 'Why is the light so wonderful?'," said Agatha Hughes, the current resident of the Vanna Venturi House, aka Mother House. "I think it's because it comes from so many places. Up above you and down below — it has so many angles and planes to play off of."

Hughes has been living here for four years, having inherited the house from her parents who resided in the house for 40 years. The house is a jangle of odd angles, curved planes, and windows layered against shortened walls.

Even on an overcast spring day, the rooms are filled with diffused light.

"I don't have a light on in the house, not one light bulb, and there's light everywhere," marveled Hughes.

The Vanna Venturi House has been on the bucket list of almost every architect in the world since it was built in 1966. It will be featured in an upcoming PBS documentary, "Ten Buildings That Changed America," premiering May 12.

The house was designed for Venturi's aging mother, who lived with a caregiver. When he designed it in 1961, the young architect was kicking against Modernism, with its clean, modular lines, and at the same time making a home where his mother would feel comfortable.

The result is a house full of crazy-quilt shapes. There's an asymmetrical trapezoid fireplace, a staircase with jutting corners, and a roof split by an empty shaft where the peak would be.

"I never find the shapes -- the complex angles and shapes -- I never find the jarring," said Hughes. "They all fit together in a beautiful way that's harmonious."

Hughes lives here full time, constantly beset by visitors from around the world. For the most part, she welcomes them, and keeps the house in show-off condition (except for the basement, a strictly private space where Hughes allows her own art practice to get messy). Sometimes visitors request a visit in advance, sometimes they show up at random times.

Welcoming visitors, setting boundaries

"It's very obvious when you come down the driveway, you can come to a certain place where you can see the entire façade of the house and you're not in my space, even though you've come down my driveway," said Hughes. "But the minute you step over that imaginary line, you are in my space, then I expect you to come to the front door and ask permission."

The house has not been altered during its 50 years. It has the original flooring, original blinds, and original cabinets. Robert Venturi has been consulted every time the house was repainted.

Upkeep is expensive. Hughes will have to sell it soon, and is trying to protect the house with historical easements to make sure the next owner will be as faithful to the architect's original vision.

WHYY will host a preview of the film "Ten Buildings that Changed America" Tuesday, with a discussion of the work of Robert Venturi and his partner Denise Scott Brown.