I would never write a poem about a salt cave. Or a "salt den," to be more specific. But if I were to do such a thing I would use many metaphors about the heart.
Something about the ocean being like a big bucket of tears, and when they dry we get all this salt, but since we adulterate our tears with plastic, then our crystalized tears contain those hyper-bits of objects of refuse.
Salt caves grow from rain water drip drip dripping. Don't touch the real drip-stones! Metaphor about being inside a broken heart that grows new hearts. They glow while growing, is how you know they're healthy, ready to try again. And this one is fake--an incubator. A cold hot house.
In the salt cave there are chairs to recline and watch the hearts grow. You can observe the new ones try tiny things, like glowing without consequence. Dig your feet into the tiny rocks of hearts. Strangest beach ever. Beaches inside caves inside a heart inside suburb.
If this were a poem the speaker, The I, would lick the wall. Just once, to test that it was real. The I would grab a handful of tiny heart rocks and eat them, to test that they were real. The I would find both to be truly salty, and comforted by the voice over telling I that salt is antiseptic and hygienic.
The I would taste limestone, dolomite, marble, and sandstone. The tiny turkeys set to brine.
Because the thing about salt caves is that they are mainly intended to enhance respiratory function. The light waves break down the salt particulates, releasing them into the air, and breathing them is therapeutic.
But if this were a poem, breathing doesn't matter, because this cave makes hearts. Hearts pump, lungs inflate. These metaphors do not mix. Like oil in salt-water. Don't you dare put oil in your tears. Hearts, young and old, cannot pump oil. Don't even try. Lick the wall again, look again to see if the pretend camera seems to be connected to an electrical source.
If this was a poem where The I licked everything, The I would experience thirsts. A dried up ocean floor on her tongue, transmutation of teeth into bleached coral, hypoxic saliva glands, sandy esophagus, so forth.
Too much salt, The I becomes a deer. The deer becomes jerky. The jerky becomes waste. The waste encounters the soil. The soil over salinates. < no I do not like this arc > Plants do not live in soil that is too salty. They die, their spirits wisp away into salt caves, where they make the tubes in the new hearts.
By god, look at them grow. The I could take at least two more significant betrayals with a heart like that.
This poem would also use words to measure time in the cave, like: forever, never, weather, treasure, tether, pleasure, leisure, seizure, and now.
Proper drainage is the only way to ensure soil does not over salinate.
Pronouns include: The I, her, you and them (them is for the hearts. The I does not recognize the singular).
Viable soil is around 15% salt. Over salted soil is highly acidic-- a ph over 8.5, it might not seem very acidic, but that's a high number for soil. (to compare, cakes are about a 5 in ph level.)
Living, human bodies carry around between 175-200 teaspoons of salt at any given moment. Blood's acidity is just under the 7.5 range. Also pretty basic. (basic like jorts, cochella and cupcake vending machines.)
The ocean ought to have a ph level at 8.2, but it doesn't anymore. (see above regarding jorts, cochella and cupcake vending machines.)
The poem would end with a refusal of The I to make a claim about breathing--the alleged reason for being in a salt cave. Avoiding a bookending of cyborgian plastic sheep dreams. No claims on the pumping out of the ocean into buckets. No.
Instead, The I would conclude with writing that there have been dreams about these glowing hearts. In this fake cave, The I tests some real thoughts about what so many glowing hearts can do. Has decided the answer is much.
This would be a terrible way to end a poem. More reasons to not write it.