(This is a short story, written in second person, intended to be read right now but remembered and fantasised about later to build arousal. So bank the bits you like and expand on the fantasy yourself later, personalize it ;) This one's focus is deep breathing, submission and relaxation, with no mention of genitals.)
After an hour of trekking, you finally find the private natural pool from your vision, with its distinctive peachy pink water. Hidden by overgrown rock walls but open to the sun, it's your personal oasis today, framed by moss and exotic fragrant flowers. It's humid down here, not too hot, just close.
Stripping to dip a toe, you find the water is the same temperature as the surrounding atmosphere, giving the bizarre sensation of moving through thicker air, not liquid. As you sink further in your feet find no bottom, it goes deep! The water feels a fraction more viscous than a normal bath, the rivulets taking longer to run down you, enough time to enjoy each tiny trickling sensation on your skin. It must contain something strange because you float effortlessly when laying back. Ears just below the surface, all sound having a warbly, far-off, echo. Aside from that, it's hard to tell which parts of you are submerged, like you're floating on a pleasantly warm uncurrent, an occasional bubble tickling along your spine as it peacefully surfaces. It feels natural to take long deep breaths here, the subtly sweet air tasting as good as it smells. Each deep belly-filling inhale raises you a little, surfacing, feeling that line where water meets air against you in a way that draws attention to any lingering tension in your muscles, then settling back in. You feel that tension resists for a second, then fade to easy stillness, far more aware of your body and serene surroundings, conscious thoughts getting less frequent, blurry.
Closing your eyes for long minutes. You're only vaguely aware of shifting in the water around you. This is a safe space, nothing could harm you, somehow you're certain. They surfaced so gracefully that you're only aware of them when hands start gently exploring your body. Lazily opening your eyes you see them, mermaids, more than you can count. This is their pool and you are a welcome guest for as long as you like.
They have a strange ethereal beauty, like this place itself, big almond-shaped eyes in vibrant colours, skin shimmering with natural waterproof oil, iridescent in the light. They smell sweet too, but distinctly more feminine. All eyes are on you, full lips curling into smiles, their smooth breasts pressing against one another as they crowd to get a better look at you. One says something poetic in a lyrical language similar to elvish, you don't understand, but the words flow into one another beautifully. They all repeat the phrase as one and their meaning sinks into you, your emotions swelling, letting you know their intent. You're safe here, let us pamper you, love you. Submit to the sweet pleasure and relax.