This house does not work for your needs. No one wants anyone going through their bedroom guest or not. it woukd be great if you needed a large office or studio!

Keep looking!

I'm sure a staircase can be added to access the 4th floor, like a hall closet? Do you have a floor plan?

My guess is someone closed the room around a staircase.

Who would know without a floor plan? Even an ATTIC would have a "publlc" hallway access.

I'd consider it for an investment. With a massive fourth floor, there'll be a way to add a stairs. Then the value will go up a lot whether you keep or resell.

This is not a bedroom and should not have been listed as one. Anything is possible with enough $$$$$$ do you have the money to under take a huge job?If not keep looking. Nursery spaces are a fleeting need almost anything can become one , I have seen them in walk in closets an actual bedroom is another thing . You need to post a floor plan here to scale and pictures if you want a bit of help. Post those here in comments . The floor plan in jpeg format DO NOT start another post Take a good contractor to the house to see what might be possible before doing anything else then if you decide to go ahead get some real prop help to do this and abey codes .

As others are saying if your budget is big enough almost anything is possible including adding a stair to the topmost floor. Would it be possible to move your master suite to that upper most floor and use the room below as a sitting room?

"Am I setting myself up for future headaches?"

No, you will have them as soon as you close on the house purchase.

Looked at a house a few years ago that had 3 bedrooms on the second floor and a fourth bedroom and bathroom in the third floor attic. Like yours it had the problem that you could only get to the fourth bedroom through the master bedroom. Even stranger you went through the master then opened a door to the stair, which was actually an open spiral stair on a little balcony open to the first floor stair below. It was one of several oddities to this house that told us to move on despite being on a great lot in a great location*

I would only consider this house if you wanted to make the 4th floor the master (does it have it's own bathroom?) or make the second bedroom your master and shrink the current master to create a corridor to the stair, making the remainder your future kid's bedroom. Otherwise, see if you can find something that works better for your current and future family.

* other quirks: the current owners had expanded the kitchen to gargantuan proportions to take over the dining room and breakfast room with 2 of every appliance. The counters were set at 42" with all of the appliances set on platforms. There was a finished and heated tacked on man cave bigger than any other living room that could only be reached by walking across the garage. And the master bathroom was being sold as-is in raw shell condition. A house rife with do-it-yourself and too-personalized conditions that ended up selling for way more than it should because of it's location.