In that case it's often best to run hard in the other design direction and celebrate it in plain sight, make the bathroom part of the plan and a piece of the experience. Celebrating "unwanted" things is one of my favorite design tricks.
A vent fan is the way to get the moisture out of the house. I repeat, out of the house. Don't get me started on how many times I've seen bathrooms vented into the attic or another hidden space. Your attic may be hot or cold, but it's still technically inside. Get that moisture outside with the rest of the clouds!
And consider the plumbing, too. While drain lines and electrical services aren't all that cool to look at, copper supply lines (water lines) can be gorgeous. If you've got an open structure, it's sometimes easiest — and awesome-est — to make the most of what you've got.
Exposing pipes can be a cool way to make a basement space feel industrial or like a man cave. It's also way easier than building soffits and bulkheads to hide everything. If you're a building geek like me, it's best to design a space where you can see the working parts.
While hollow-core doors can be fine for certain rooms, I try to use solid-core doors for the bathroom to keep the bathroom experience as much of a one-person affair as possible. Solid-core doors deaden the sounds created in the bathroom. So if you're having a book club meeting or poker night down there, a solid door and insulated wall framing that both deaden sound are nice for everybody.
So when I go into a small space, I'm always thinking about how I can use it smartly, use it vertically and make everything look like it's supposed to be there.