I've been watching some old episodes of Leave It To Beaver from around 1960 and am blown away to see none other than The Munsters home in the neighborhood years before it was used for the TV show.
Even complete with the rod iron gate around it. It definitely has the creepy feel to it even then.
I always thought it was built specifically for The Munsters.
The house exterior was built for the 1946 film So Goes My Love. It was disassembled and put into storage, then revived in the early 1950s when Universal decided to construct a residential street which could be used for various movies and tv shows at less cost than custom-building.
Wikipedia has a good history of the Munster Mansion, including a list of the productions in which it can be seen.
The indoor scenes were filmed on a soundstage. The iconic house was an external set - the only interior fixtures were whatever could be seen from the outside, so they may have had a mock-up of the stairs behind the door but not much more. All the internal sets would have been struck shortly after the series was canceled.
If you watch the reruns enough, you can get a feel for the layout of the house. The door opened to the foyer with the grand stairway. Through the door, the living room was to the left. The dining room behind the living room. The kitchen was behind the foyer. In some scenes, you can see the stairway through the doorway to the kitchen. They never seem to show what areas are to the right of the front door. From the exterior set, there's clearly a room there, but the interior is never shown.
Some day I'd really like to take the tour of the replica Munsters Mansion in Texas. It would be interesting to see what the designers did with some of the unaccounted for spaces.
The "actual house" is an empty shell. Basically, there's nothing in it other than probably some sort of supporting structure to keep the facade standing. That's the whole point of all the houses along Universal's "Colonial Street" - they're "external sets" used to create the illusion of houses.
A couple named Charles and Sandra McKee built an exact replica of the Munster mansion in Waxahachie Texas (about 25 or so miles south of Dallas). They painstakingly recreated the interior room by room by watching and re-watching episodes of the series. They even have actual items from the show in this house. The McKees live there full time.
The house is open to visitors only once per year though, although you can stand at the iron gate and look in at any time (I visited, but unfortunately not when the house was open).