I try to find museums in UK that don’t contain words “art” and “nature” (case-insensitive) in item in english language.
And 2nd query the same, only to find the words “art” and “nature” in description.

I would also like to know what the same query would look like, but containing the words “art” and “nature”.

I think this query is correct, I just need to improve it:

SELECT ?item ?itemLabel  ?itemDescription ?coordinates WHERE {
  ?item wdt:P31/wdt:P279* wd:Q33506 ;
        wdt:P625 ?coordinates .
  ?item wdt:P17 wd:Q145 .
  SERVICE wikibase:label { bd:serviceParam wikibase:language "en" } .
}