There is nothing esoteric about topos theory, it is a formally defined concept: https://en.wikipedia.org/wiki/Topos https://en.wikipedia.org/wiki/Topos Thought

There is nothing esoteric about topos theory, it is a formally defined concept: https://en.wikipedia.org/wiki/Topos https://en.wikipedia.org/wiki/Topos Thought it was important to state this, as Grothendieck also wrote rather esoteric texts, Récoltes et Semailles as well as La Clé des Songes, which haven't been translated or even published.