Ohne Navi hätten wir die Einfahrt zum Parkplatz fast verpasst.

Because Ohne Navi sets the condition for the whole sentence: without GPS / without a sat nav.

German often puts this kind of phrase at the beginning when it gives important context. It is similar to English:

• Without GPS, we would have almost missed the entrance to the parking lot.

Starting with Ohne Navi emphasizes that the GPS was the reason they did not miss it.

Ohne usually takes the accusative case, but in this sentence Navi appears without an article, which is very common in German when talking about something in a general, practical sense.

So:

• ohne Navi = without GPS / without a sat nav
• ohne ein Navi = without a GPS device (less idiomatic here)
• ohne das Navi = without the GPS (a specific one)

Using no article here sounds very natural, much like English often says without GPS.

Ohne always takes the accusative.

So in this sentence:

• ohne Navi

The noun after ohne is in the accusative. You cannot see a form change here because Navi is a neuter noun and, without an article, its form stays the same.

Other examples:

• ohne den Mann
• ohne die Frau
• ohne das Kind

This is the Konjunktiv II der Vergangenheit, often used for unreal past situations or hypotheticals.

Structure:

• hätten
  • past participle

Here:

• hätten = subjunctive form of haben
• verpasst = past participle of verpassen

So:

• hätten wir ... verpasst = we would have missed ...

This tells you the speaker is talking about something that almost happened but did not actually happen.

Because the sentence begins with Ohne Navi, which takes the first position in the clause. In a German main clause, the finite verb must come in second position.

So the structure is:

1. Ohne Navi
2. hätten
3. wir
4. the rest of the sentence

That gives:

• Ohne Navi hätten wir die Einfahrt zum Parkplatz fast verpasst.

If the sentence started with wir, then it would be:

• Wir hätten ohne Navi die Einfahrt zum Parkplatz fast verpasst.

Both are correct, but the emphasis changes.

Fast means almost.

So:

• fast verpasst = almost missed

In this sentence, fast is placed before the past participle verpasst, which is very natural in German.

Compare:

• Wir haben den Zug fast verpasst. = We almost missed the train.
• Er ist fast eingeschlafen. = He almost fell asleep.

It is modifying the whole idea of missing the entrance, not just one single word.

Die Einfahrt here means the entrance / driveway / way in, specifically the point where you turn into the parking area.

In this sentence:

• die Einfahrt zum Parkplatz = the entrance to the parking lot

Be careful: Einfahrt can mean slightly different things depending on context:

• a driveway to a house
• an entrance road
• the entry point to a parking area or garage

Here it is clearly the place where the car should turn in.

Because die Einfahrt is a noun, and it needs a phrase describing what it leads to.

• zum Parkplatz = zu dem Parkplatz = to the parking lot

So:

• die Einfahrt zum Parkplatz = the entrance to the parking lot

If you said in den Parkplatz, that would sound odd because in German you normally say:

• auf den Parkplatz fahren = to drive onto the parking lot
• zum Parkplatz = to the parking lot
• die Einfahrt zum Parkplatz = the entrance to the parking lot

So zum Parkplatz is the natural complement after Einfahrt here.

Zum is a contraction of:

• zu dem → zum

Since Parkplatz is masculine (der Parkplatz), zu dem Parkplatz becomes zum Parkplatz.

This contraction is extremely common in German.

Examples:

• zum Bahnhof = to the train station
• zum Supermarkt = to the supermarket
• zum Parkplatz = to the parking lot

The verb is verpassen.

In this context, verpassen means to miss in the sense of failing to notice or reach something in time.

Examples:

• den Zug verpassen = to miss the train
• die Ausfahrt verpassen = to miss the exit
• einen Termin verpassen = to miss an appointment

So:

• die Einfahrt ... verpasst = missed the entrance

It is a very common everyday verb.

Yes. If you just wanted to state a real past event, you could use normal past or perfect forms instead of hätten ... verpasst.

For example:

• Ohne Navi haben wir die Einfahrt zum Parkplatz fast verpasst.

That means:

• Without GPS, we almost missed the entrance to the parking lot.

But your original sentence is slightly different in tone:

• Ohne Navi hätten wir ... fast verpasst.

That means:

• Without GPS, we would have almost missed ...

So the original emphasizes that the GPS prevented the problem.

Yes. In everyday German, das Navi is a very common short form of das Navigationsgerät or simply the navigation system/app.

Depending on context, it can mean:

• a standalone sat nav device
• a car navigation system
• a phone navigation app

So in natural English, it may be translated as:

• GPS
• sat nav
• navigation system

All are possible depending on the variety of English and the context.

Because in this kind of clause, the finite verb is hätten, and the past participle goes to the end.

So the pattern is:

• hätten
  • subject + other elements + verpasst

This is standard German word order for perfect-like or modal-like verb structures.

Compare:

• Wir hätten den Zug verpasst.
• Sie hätten uns gesehen.
• Ich hätte das gemacht.

The final position of verpasst is completely normal.