Door in a kneewall
It greatly depends on how you plan to finish the walls. Plain painted drywall - no way, door will show. If you plan to wallpaper, and use a pattern with dark vertical lines, making the door so its edges coincide with lines will work well. If you are putting up T&G paneling or beadboard, a concealed door is a no-brainer. You can use euro style cup hinges, and for handle: One REAL clever way I've seen is drilling the door from opposite side almost all way through with a forstner, and gluing a magnet in the recess. Invisible from front, but placing a piece or steel or iron in the right place creates a 'handle'