To create a luxurious retreat in your bathroom, consider upgrading fixtures such as faucets, showerheads, and bathtub. Install a spacious shower with multiple showerheads or a soaking tub for a spa-like experience. Incorporate high-quality materials like marble or granite countertops, and add underfloor heating for added comfort. Additionally, ensure ample storage space by installing cabinets or shelves and invest in quality lighting to create a relaxing ambiance.