Adjust the lighting in your bathroom to cast a nice glow on your bathtub.
If necessary, turn off the lights altogether and spread candles all around the outside of the bathtub. You can also put them on the floor or on the bathroom counter. Use small tea light candles to add lots of light and ambiance to make the bathtub appear romantic.
Sprinkle flower petals around the outside of the bathtub, in the water or around the candles.
Use soft and romantic colors like pink, white or red. You can also put fresh flowers in vases and spread them around the bathtub.
Add aromatic bath beads or bubble bath to the bathtub.
Scents like lavender, rose, vanilla or amber tend to have soft and soothing fragrances that can add to the romance of the bathtub and your experience.
Burn some incense at the foot of the bathtub to add more fragrance to the room.
Use a scent like sandalwood or cedarwood to add a sweet, earthy smell that can enhance the romance of the bathtub through aromatherapy.
Put a loofa or a soft sponge in the bathtub that you can use to wash one another.
You can also fold up fresh washcloths and arrange them on the side of the bathtub with some flower petals sprinkled on top.