It might just be a fun entrance that they made for their kid. It doesn't need to have a purpose.

But I'd love to see a picture of it.

I would think it is for storage or access to a crawl space. Have you looked inside?

Beautiful woodwork. I hope you aren’t thinking of painting it.

If the house has been added onto on the bedroom side, maybe it used to be a window opening & the door was added to cover the hole just for S's&G's?

Do the stairs go into the basement? It could be a shortcut between the playroom in the basement and a kids bedroom so that they don't have to go through the main section of the house.

Maybe the parents liked to have dinner parties and got annoyed with kids running back and forth between the two rooms.

It's not behind a bathroom is it? These little doors are also used to access the plumbing for tubs, showers etc.

He said it goes into a bedroom.

What's inside? Could it be a chute for dirty clothes?

Is the laundry in the basement? Maybe it was to pass clothes through? Is there any kind of shelving inside or is the other opening right behind this one? Does the bedroom door have this same nice woodwork on it? Is that door the same distance up from the floor?

Open the door and take a pic! Very curious.

>>He said it goes into a bedroom.

Oh, duh, bad reading comprehension on my part! Makes more sense now.

Maybe it was for passing or retrieving something like laundry without going in and out of the room?

An entrance for a legless person? [I'll let myself out!]

It's possible it was a door to a linen closet that used space in the bedroom. Perhaps the enclosed closet area was removed to make more room in the bedroom? Is it a small bedroom?

Where is the bedroom door located? Could this be an emergency exit?