malcolmissimo: Thanks for pointing out the distinction, but i think that for your final observation you're using the wrong yardstick. I'd say that most Americans are quite clear about the difference between yards, courtyards, farmyards, and gardens-- the last of which are cultivated throughout the country, irrespective of region, and where 'garden tours' highlighting an area's most beautiful are annual events.
Or should it?
La corte o cortile è uno spazio scoperto di un edificio, al fine di dargli maggior luce e aerazione. (The court or courtyard is an open space of a building, in order to give more light and ventilation.)
(architecture) An internal courtyard, surrounded by walls but open to the sky
"cortile internal court surrounded by an arcade, ..."
See also: Google Images result for cortile which shows that although some may incorporate gardens, many do not. Which, to me, strongly suggests that garden should not be accepted as a translation for cortile.
"Court yard" is another option I think since the two words are very similar. In the US you might also hear "back yard" instead of just "yard" since generally speaking, "yard" could imply the "front yard" and I can't imagine anyone eating in their "front yard". "Back yard" picnic or barbecue for example is very common.
Grammatically it'd be correct (as I suggested a year ago!) or when spoken with the intonation of a suggestion, but DL usually signals a "Let's do X" sentence with an exclamation point rather than a period. I don't know if this was a "Type what you hear" sentence or a translation b/c DL uses the same sentence in several different exercise types: listening, translation Italian > English, English > Italian, and multiple choice, but as I said, your answer (sadly like mine! ) probably wasn't accepted b/c DL did not consider it a "Let's do it" type of sentence.
OLR92: With certain stock phrases, the definite article is not used -- nel being a contraction of 'in' + 'il'. So e.g. 'in banca', 'in palestra', 'in casa' etc. That said, I don't know of any specific rule which will tell you which place terms require the article and which do not. Given that it's also 'in cucina' it seems to me that most of these involve feminine nouns, so it's not "nella" but simply 'in'.