Learn Hardcore German: Wir übernachten im Zelt am See. - We stay overnight in the tent by the lake.

schlafen = to sleep (the act of sleeping, no location implied)
- Ich schlafe. – I am sleeping.
übernachten = to spend the night somewhere (focus on where you stay)
- Wir übernachten im Zelt. – We are staying overnight in the tent.
bleiben = to stay/remain (not necessarily overnight)
- Wir bleiben am See. – We are staying at the lake (could be for the day).

So übernachten combines the idea of sleeping with staying somewhere for the night.

Is übernachten a separable verb? Do I ever split it like über + nachten?

No. Übernachten is not separable; it is an inseparable prefix verb.

Present tense:
- Wir übernachten im Zelt. (not Wir nachten über)
Perfect tense:
- Wir haben im Zelt übernachtet. (the participle is übernachtet, not genachtet or übergenachtet)

Even though über- can sometimes be a separable prefix in other verbs, in übernachten it is inseparable and always stays attached.

What does im in im Zelt stand for, and why not just say in dem Zelt?

Im is simply the contraction of in dem:

in dem Zelt → im Zelt
in dem Haus → im Haus

You can say in dem Zelt, but native speakers almost always use the contracted form im Zelt in normal speech and writing.

Grammatically, in here takes the dative case because it describes location (where we are staying):

das Zelt (neuter) → dem Zelt in dative → im Zelt

Why is it am See and not an dem See or im See?

Am is the contraction of an dem:

an dem See → am See

You can say an dem See, but again the contracted am See is standard and more natural.

The preposition an means “at/by” (next to, on the shore of), so:

am See = at the lake / by the lake (on the shore or nearby)

Im See would mean in the water of the lake, literally in it, e.g.:

Wir schwimmen im See. – We are swimming in the lake.

In your sentence, you are camping by the lake, not floating in it, so am See is correct.

Which case is used in im Zelt and am See, and why?

Both im Zelt and am See use the dative case.

im Zelt = in + dem Zelt (dative)
am See = an + dem See (dative)

Reason: in and an are two-way prepositions (Wechselpräpositionen).
They take:

Accusative for movement into a place (where to?)
Dative for location (where?)

Here the sentence is about where we stay overnight (location), so it uses the dative:

Wo übernachten wir? – Im Zelt am See.

What genders do Zelt and See have, and how do the articles change?

Zelt is neuter: das Zelt
- Nominative: das Zelt
- Dative (singular): dem Zelt → contracted im Zelt (in dem Zelt)
See in this meaning (“lake”) is masculine: der See
- Nominative: der See
- Dative (singular): dem See → contracted am See (an dem See)

Be aware: die See (feminine) exists too, but it means the sea (as in “the high seas”), and is used differently, often in fixed expressions (e.g. auf See = at sea).

Why is the verb in second position: Wir übernachten im Zelt am See, and can the word order change?

Standard German main clauses have the finite verb in second position (the V2 rule).

In your sentence:

Wir – first element (subject)
übernachten – verb (must be in second position)
im Zelt am See – rest of the information

You can move another element to the front, but the verb must stay second:

Am See übernachten wir im Zelt.
Im Zelt übernachten wir am See.

All of these are grammatically correct. Changing the order slightly shifts the emphasis (what you want to highlight first), but the basic meaning remains the same.

Is it more natural to say im Zelt am See or am See im Zelt? Is there a rule?

Both are possible:

Wir übernachten im Zelt am See.
Wir übernachten am See im Zelt.

A common tendency in German is to move from general → more specific for locations:

am See (general area)
im Zelt (very specific spot where you sleep)

So many speakers find Wir übernachten am See im Zelt slightly more natural because it goes from the broader place (lake) to the exact place (tent).

However, Wir übernachten im Zelt am See is also very common and perfectly correct; here am See is acting more like extra information specifying the tent.

Can Wir übernachten im Zelt am See also mean a future plan, like “We will stay overnight in a tent at the lake”?

Yes. In German, the present tense (Präsens) is very often used for future plans, especially when the context makes it clear:

Morgen übernachten wir im Zelt am See.
= Tomorrow we are staying overnight in a tent at the lake.
(In English you might say “are going to stay” or “will stay”.)

If you really want to highlight the future, you can use werden:

Wir werden im Zelt am See übernachten.

But in everyday speech, present tense with a time expression (morgen, nächste Woche, etc.) is completely normal for future meaning.

How would I say “We stayed overnight in a tent at the lake” in the past tense?

The most natural everyday form is the present perfect (Perfekt):

Wir haben im Zelt am See übernachtet.

Breakdown:

Auxiliary: haben
Past participle: übernachtet

The simple past (Präteritum) is also possible but is more typical for written narrative:

Wir übernachteten im Zelt am See.

For spoken German, Wir haben … übernachtet is what you will hear most.

Could I replace übernachten with schlafen in this sentence?

You could say:

Wir schlafen im Zelt am See.

This is grammatically fine, but the nuance is different:

Wir übernachten im Zelt am See.
→ Emphasises spending the whole night there; it sounds more like a plan or an arrangement (e.g. camping).
Wir schlafen im Zelt am See.
→ Focuses more on the act of sleeping; it could be for a nap or for the night, depending on context. It does not automatically imply “overnight” as strongly as übernachten does.

For camping or staying somewhere for the night, übernachten is the more precise verb.

How do you pronounce übernachten, especially the ü and ch?

Syllables: ü-ber-nach-ten
The ü is like the German u with your lips rounded but the tongue in the position of English ee (as in see). A rough English approximation is between ee and oo, but there is no perfect English equivalent.
The ch in nachten is the ach-sound, like in Nacht, Bach, or Scottish loch. It is a throaty, voiceless sound made further back in the mouth.

Approximate pronunciation: [ˈyːbɐˌnaxtən].

Why do we say wir and not uns here?

Wir is the nominative form of the first person plural pronoun: we (subject of the sentence).

Uns is:

Accusative: direct object (e.g. someone sees us)
Dative: indirect object (e.g. someone gives something to us)

In your sentence:

Wer übernachtet? – Wir. (Who is staying overnight? We are.)

So the subject must be wir, not uns:

Wir übernachten im Zelt am See. ✔
Uns übernachten im Zelt am See. ✘ (ungrammatical)

Is there any difference between am See and something like am Meer?

Yes, they refer to different kinds of water:

der See (masculine) → am See = at the lake
das Meer (neuter) → am Meer = at the sea

So:

Wir übernachten im Zelt am See. – We are staying overnight in a tent at the lake.
Wir übernachten im Zelt am Meer. – We are staying overnight in a tent at the sea.