When my husband took me to a squinchy Japanese restaurant that had high chairs at a bar-style counter, the server laconically instructed me to put my bag “downstairs”, which meant “on the shelf under the seat of the chair”.
I have heard English teachers eager to hold students accountable for their spoken language deride this common Singlish use of “downstairs”, but it’s wonderful (and typical) in its succinctness.
If you use the preposition “under”, you have to include a noun for the preposition to be, well, positioned in front of. If you use the adverb “downstairs”, you’re just saying something needs to go below something else, and letting context do the work of indicating what the something else is.
Chinese has a phrase approximately meaning “down side” which can be used the way the server was using “downstairs” to adverbially indicate “under something”. It also has phrases meaning “up side”, “behind side”, “opposite side”, etc., and you can say “located opposite side” without needing to say “located opposite the hotel”, for example, the way we can say in English that “the receipt is in the bag” or just “the receipt is inside”.
I get the sense that Chinese relies on context more than English, or at least relies on context in ways that English doesn’t, since a large proportion communication in any language is always shared context.