That's interesting! Thanks for letting us know! I love that film and love learning about sets and locations!

The house used for the exterior shots still exists, though it has been remodeled and a large wall and gate have been put up in front. For the really curious, you can drive by or Google map it: 9271 Robin Drive, Los Angeles. Please don't disturb the occupants.
Alas, the real interior is nothing like the film interior.

In an interview from 2008 with Blake Edwards & Gavin McLeod, Gavin said the exterior shots were of a house "way up in the hills in the Truesdale Estates" in Beverly Hulls.

Most likely, the facade was a fake as well.

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Hello.
I wanna make a floorplan of this amazing house.
I know that all the interiors are filmed in a soundstage including the backyard with the pool and garden.
But there are some sequences of the fronthouse (at the beginning when Peter Sellers comes to the house in his tiny car and at the ending when leaves it) aparently filmed outdoors.
Is this a fake facade too or is a real house ???
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Here's the answer to your question: The movie was shot on the MGM backlot (before it was torn down to become condos.) That's it. No house was used.