It is unclear if the Horcrux works only when it comes into contact with a human, or if it does its job anyway. If the second is true, then make a few - and send it into space, to the bottom of the ocean, etc. If the former, then one or more books in the public library. Not the most demanded (so as not to plague anyone's eyes once again), but valuable enough (so that sometimes they are still taken). Any highly specialized monographs, etc. If / when I have a khan, then not right away, but within one or two years someone will probably pick them up, and ...
I will not speak for myself, but I think many will be interested to know what Daniel Radcliffe, the performer of the role of Harry Potter, would put a piece of his soul into. When asked by a fan "What would Harry use as a Horcrux?" my iPod, but then I decided I would put a piece of my soul into an important music album for me on my iPod, like 'Ziggy Stardust and the Spiders from Mars'.
For example, in some terribly protected nature reserve in a huge oak or ship pine. Go, look for a tree in the forest, and try to guess which one is wrong :)
Many people forget that the Horcrux is part of the soul. It cannot be sent into space or hidden so that it cannot be reached. And according to the magical laws, the split souls are trying to reunite, emitting dark magic, just like at the moment of the creation of the Horcrux, which gives them away.
The most reliable way, as history confirms, is to hide it where no one will become look for him, under the nose of the main enemy (if there are any, maybe you just want to live longer without trying to overthrow the ministry). Otherwise, you can just turn on romance. In this case, I would put mine in the Trevi Fountain, I really like it, as a bonus, it is always surrounded by Muggles, which will protect it. And if I was carried away by the breaking of the soul, then according to the same scheme I would choose a place: constantly surrounded by Muggles and of historical value.
(My friend joked about a red-haired man, like no one would look for a soul in them)
I'm not sure that this is possible, but if it is possible then:
-Atom of oxygen or some other gas that is not subject to decay.
-Large space body, which predicted to exist for a long time, for example: a recently born star.
None. I am a Buddhist and dividing what in principle does not exist (the soul) to create Horcruxes is meaningless for me. But there is a cooler recipe: you can grow such karmic fruits so that the next incarnation is more favorable than the current one. : 3 Since, instead of the soul, the Buddhist Teaching has kindly provided for people like me, the imprints of our deeds in the mind :) And this is stronger than Horcruxes))
I would create a horcrux in the form of a picture (perhaps something from the series of Darian Gray, but not so mystical as not to attract too much attention). The Horcrux must be hidden, and the best way to hide something is to put it in a prominent place.