Pictures help. Take them outside and inside the room best to keep doors closed on rooms you don't want people in

I think that the best way is to direct your guests to the appropriate area. A "washroom" sign with an arrow that matches your design style would work well. Or a sign on the door of your room that says "This is NOT the Washroom!" with an arrow. A tour as mentioned above would help but might not be super do-able if you host a lot of open house type parties. You could also take your guests' coats at the door and clearly say, "I'll just lay this on my bed" as you go to do just that. Or position a chair in front of the entrance to your room.

Realistically, do you often have guests at your home for the first time though? It is a mistake that will only be made once per person! I know when I'm at a home for the first time I always ask the host "where is your washroom?" I don't go wandering the house poking my nose into random doors!

:-D

Oh, for the lighting issue: LED strip lights at the floor level.

I would decorate it a bit like I would the bedroom. A wedding picture, some candles, the intimate little sculpture you have there. Things that give it the feel of "entrance to the bedchamber." Maybe some hooks for you personal everyday things, like keys and a charge station. If it's well-lit, it will only be more inviting, so I would stick with something dim. :)

Decor *and* behaviour modification; you do want both.

For the wall, poi ting in the direction of the guest bathroom:

https://www.etsy.com/ca/listing/605597937/bathroom-arrow-wood-sign-wood-sign-art?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=bathroom+arrow+sign&ref=sr_gallery-1-19&organic_search_click=1#

https://www.etsy.com/ca/listing/571776054/sign-restroom-wedding-restroom-bathroom?ga_order=most_relevant&ga_search_type=all&ga_view_type=gallery&ga_search_query=bathroom+arrow+sign&ref=sc_gallery-1-2&plkey=a835f4c96e0b1f058d0a007059d972f86d902f4f%3A571776054#

And for your bedroom door:

If it were my home I would have some fun with this space. I would hang a picture of the Gone With the Wind movie poster in the wall inset with a picture light and set a few Gone With The Wind plates/sculptues/figurines/something and a couple of old movie tickets on the shelf. I would then buy and hang one of the old fashioned deep red, velvet ropes they used in the old theaters accross the threshold when company came by. It would keep people out and be a conversation starter.

I’d fix the doorway and move the door. Signs? Yes, in filling stations!

For big/dramatic effect, I'd paint a mural of the night sky on the walls and ceiling of your alcove, then maybe put up tiny led lights.

On a smaller scale, maybe paint the inside of your niche a dark blue with either a gold vinyl decal with something like "Dream a Little Dream of Me" or set one of the small moon globe lights on the shelf.

Without knowing what colors or decor style, it's hard to say if these would be effective or jarring.

Carol

Well, the answer on what to do there will depend on what you want to spend. Ultimately that small dated opening needs to be fixed. That arched doorway needs to be removed and opened up, and that dated niche on the wall needs to be drywalled over. But regardless of whether you do that or not, that space is not big enough to "decorate". So I would simply hang a long piece of artwork on the niche wall (to cover it if you aren't going to drywall over it). And then I would put lighting strips behind the art to provide some light in that tiny space and to further highlight the art piece. Do not hang bathroom signs in your home. No. All you need to do is simply let guests know when they first enter your home where things go and where things are. I say something like "please feel free to put your things here (and I point to the table and accent chair I have in my entry way) and "the restroom is down the hall on your left if you need that". If you tell people what you want them to do, they will usually do it and they will appreciate the direction instead of wondering how to be in an unfamiliar space when it is easy to feel awkward.

If this was a recurring issue with guests in my home, I would simply keep the bedroom door locked when I had company. I'm surprised they don't ask where the bathroom is if they are new to your home. I think decorating that alcove will lead people to it even more.

"Signs? Yes, in filling stations!"

Lol. It wouldn't be my choice either, and I'd just let my guests who were too rude or shy to ask about the toilet walk into my bedroom once and learn the lesson for themselves.

But the OP specifically asked for decor ideas to guide guests away from their bedroom and towards the bathroom. Signs are the only effective way of doing that if the guests are so silly they repeatedly walk into the bedroom instead of the bathroom.

To clarify, I think OPs should only hang the washroom signs while they are entertaining, they would not be hanging up full time :-D

A sign PRIVATE on the bedroom door ? I would , as a guest in your house, be intrigued by the cute little mysterious alcove and door. :)