The design of a small private bathhouse involves creating a comfortable and relaxing environment for patrons. Key considerations include layout, privacy, comfort, and aesthetic. The layout should accommodate various amenities like hot tubs, saunas, and massage areas. Privacy is crucial, often achieved through separated cubicles or private rooms. Comfort is enhanced with high-quality materials, good acoustics, and efficient heating. Aesthetics can range from minimalist to luxurious, depending on the target market.