Basement is the place of a house which is most unattended or neglected while we are busy taking care of the rest of the menage. In some houses basement is used as offices or wine cellars or even a guest room. Using your basement as a fully furnished bathroom is one of the best options you can have. For a vintage half bathroom look, you can add the basic fixtures and a toilet. If your budget permits, you could try vinyl flooring and elaborate lighting to compensate the absence of natural lighting.
For a modern habitat, basements usually do not have ample space to move freely. Even then, you can make innovative arrangements e.g. you can arrange your plumbing into one wall to facilitate locating out the piping in case of any leakage, you can use mirrors with back storage unit where you can keep your toiletries organized. If you are lucky enough to be an owner of a large basement you can try a walk-in-shower to make your bathroom a refreshing crook.
Various ways are there from which you can opt for the best possible one. A basement bathroom can be turned into a spa bathroom as it is a shadowy corner of any house. Lack of gaudy lighting gives you a room for making a mystic spa-like ambience by using artificial lighting.
For using your basement as a bathroom as a luxuriant oasis or a relaxing spa you can get various ideas from online home decor portals or even magazines. If that is not sufficient consult an interior decorator who can give you useful concepts of furnishing your bathing space.