saw this and thought you might be interested in some ideas:
http://www.houzz.com/ideabooks/query/studio-space

gozo, beautiful wood floor. Your studio has a very nice, clean and simple design. I like it. :)

An alternative to mural is an art piece like this. If you put it above your couch it will provide perspective and depth and will visually expand your space. You can have it printed in any size, on canvas, acrylic or metal... Raisa

Yes it's a great idea - I just am having trouble finding where things like this exist. I would want something that is like a NYC scene to make it seem realistic .

I'm going to research for you but you can find amazing wall murals like wallpaper of,scenes of new York and other cities will post when I find

http://www.jwwalls.com/search/product?product_id=brooklyn-bridge&query=new+york

Love the painting suggestion above. You need some depth. Add colour and mirrors too

Gozo, since you first said you wanted an illusion of another room, I thought, any abstract illusion of space in general might work as well. But you now want an illusion of a whole city :). You are probably thinking of something like this, except it is not NY but a boardwalk view in Saint-Rafael, French Riviera :) ...which may also work if you beleive you are a citizen of the world who just happens to reside in NY :)... Raisa

Dear All - Thanks for all your suggestions. I have spent a lot of time on the web, looking and thinking and re-thinking. I thinnk I might get tired of just a photo , even one with dimension. My original thought was that with two windows looking out over the city, it would be "artificial" to create a third window in the niche with a photo of something else, like the beach scene, I am more tempted now by some neat art but something with depth and dimension. OR, another thought is to have a simple trompe l'oeil double door closed, on which I could then hang a painting. Don't know if that's clear. What I didn't say in my original message was that my space is only 300 sq feet, including bathroom. It is a shoebox - a rectangle shape. Opposite the picture I posted with the mirror, niche and couch, is my murphy bed that has shelves on the front (it swivels around and then the bed comes down), plus a tiny kitchette. The two windows are at the end (short side of the rectangle.). So it is soooo important to create the illusion of more space and depth...... All your suggestions are helping me to clarify my own thoughts - keep your comments coming. Thanks.

How about a historical panoramic map mural of NYC in black and white? http://www.worldmapsonline.com/historicalmaps/new_york_1873_panoramic_wall_map_mural_grey.htm

Here is another idea if you want to have a nature-inspired art without overwhelming your space with detail or color. We can also adjust colors before printing, if needed.

FYI, all our art prints and art cards are now on sale! You will receive a 20% discount on our artist's commission now through 05/15/2013 when you enter this code at check out: JAEPJJ
Good luck finishing your room!... Raisa

Useing any scenic shot you like, have your own mural done; apply it to the niche wall; frame the wall like a window (you can use plastic mounding glued to the mural); hang a decorative rod and long drapes at the sides; put the sofa back in there...Voila - new window!
http://www.muralsyourway.com/cities-cityscapes-murals/new-york-street-scenes/

ps. you could use a picture taken of a spacious terrace, with the cityscape beyond, then you could treat the full-length mirror like a glass door to give the illusion of an outdoor space through the looking glass.