Depends on ur budget!

Radius cabinets and furniture feet

In all seriousness, Kymberly is right, depends on what you have to spend. With all that space, you could turn that into a beautiful, spa-like room. If your budget is small, I'd still paint, tile the floor - that is carpet, right? I personally detest carpet in a bathroom. I'd also replace the vanity tops. These would look great with the bowl sinks that sit on top. Maybe paint the vanities?

Paint the cabinets black change the floor for something white ....paint the walls gray or a very soft blue

Would you keep the door and fireplace or use the real estate for other purposes?

Have to say I see this space very modern with sleek, clean lines and fresh, soft colors. Physical changes dependent on budget. More natural light would be great.

Do you have enough light by the sinks? How private is the backyard? Here two inspiration shots.
I don't know your style preference and budget, but the yellow needs to go and the softer colors make things look more cohesive. Smaller mirrors with a more pronounced frame will make the place less stark and hollow.
The second shot features one large window by the tub, that by the way match the first shots' mirrors. Here a darker floor. You can now have tiles that look like wood. Lots of potential with your bathroom here! Best of luck.

jbrillant, I agree with lilion (especially about the carpet). The yellow should go. Depending on the budget, new tiles (floor and shower), new cabinets, new counter tops, new lights, new doors :) --