We don't have a huge bedroom but wanted to add a walk-in closet. We placed the IKEA wardrobes so the window could be opened. Because of the window, we could not add a door (which is not too bad).
Here you can see how we placed the wardrobes (called PAX) in a kind of U-shape.
Add chipboard to the wardrobe and put wallpaper on it. Paint it in whatever Color you like - your landlord won't mind because ist can be easily removed.
You can see a litte better how it was done in our other room where we disguised a shelf with the same method.
From the outside is will look like a normal wall, you can even hang pictures or mount something else.
Even from the bed you don't see that it is a wardrobe (but some neighbours have a clear view of our underwear...)
We added lights triggered by a motion sensor on the inside. As long as you move, there is light. One minute after leaving the light is switched off auomaically.
Have creating it for yourself. If you need more inspiration, check out my other guides in the home category: https://snapguide.com/search?topic=home&q=martin+storbeck