Translation:In the vacation home we are eating apples.
There are three main structures for clauses in German-- verb second, verb first, and verb last. Verb last structure is mostly used for dependent clauses, like "He eats because he is hungry" (Er isst, weil er Hunger hat.) Verb first structure is used for questions (Hat er Hunger?) and commands (Geh' weg!) Verb second structure is the most common. The place of the verb is not affected by the order of other things in the sentence-- if a prepositional phrase comes first, the verb comes second. If a noun phrase comes first, the verb comes second. If an object comes first, the verb comes second. Etc.
This is why you can rewrite this sentence as "Äpfel essen wir im Ferienhaus" or "Wir essen Äpfel im Ferienhaus". Does that make sense?
This is a great explanation. I just want to clarify that when saksxalmo says that verb comes second this means it comes in the second place, but it doesn't necessarily mean it will be the second word.
- example: "Nein, der alte Mann kommt nicht nach Hause." http://german.about.com/library/weekly/aa032700a.htm
In the UK the term holiday home and indeed the word 'holiday' would always be used rather than vacation, as that is an American term. It would clearly be understood but people, especially 'up North' would look at you as if you were crackers(mad), or American, or both :-)
Likewise, Americans would understand crackers. If you are crackers, you are bonkers. But if you are a cracker, you are white. And if you are mad, you are most likely Angry, unless you're a madman.
If you do come to the US on holiday, don't worry too much about using any of the words "wrong." People will know from your accent and will probably find the whole thing quite charming.
It's just that the article is required - as far as I know there's no special explanation and that's just the way it is (but there could be some grammar rule about "in" that I know intuitively rather than intellectually). It's the same as how you'd say "in the house", not "in house", or "on the mountain" instead of "on mountain", or "on the beach" instead of "on beach", etc.
("At home" is fine without an article, but "vacation home" requires the article because it's more specific - in this way it's more like "house" than "home" ["at house" is incorrect]. And "in home" is incorrect either way, anyway.)
There's two reasons that "vacation place" doesn't work. The German is referring to a cottage (in the American sense)/holiday home/holiday house specifically. Also, "vacation place" isn't natural English; it sounds like an overly-direct translation. There's even less explanation for this - it makes grammatical sense, but for whatever reason, it just isn't something that native speakers say. "Tourist spot", "vacation spot", or less commonly "holiday spot", are better options that carry some of the same meaning, but again, the German is asking for a house specifically. If you have a cottage on Lake Superior, that's only one of the many holiday homes at that particular vacation spot.
There must have been something else wrong with your sentence, because I've used "we eat apples" in my answers for this sentence and been marked correct. Sometimes Duo flags the wrong thing as the mistake - that could have been what happened to you.
I'd say that a bach is always at the beach (or at least in a beach town, The Mount or Raglan or somewhere), or maybe at Lake Taupo at a stretch. A holiday/vacation home is more generic and could be at a ski resort, out in the country, or pretty much anywhere else one holidays.
Vacation homes, airplanes, maids . . . the German Duolingo team grew up and lives in a different world than me. And, as an American, vacation homes exist (California), but summer homes (Northeast & Midwest), winter retreats (Florida & Arizona), and holiday homes (usually but not always a rental) are all used. It just depends on the region and what you grew up with.