A kulcsot a recepción hagyom, mielőtt elmegyek.

Because Hungarian usually drops subject pronouns when the verb ending already shows who the subject is.

• hagyom = I leave it
• elmegyek = I leave / go away

So én is not necessary here. You would add én only for emphasis or contrast, like I (not someone else).

Kulcsot is the accusative form of kulcs (key).

The accusative marks the direct object of the verb — in other words, the thing being left.

• kulcs = key
• kulcsot = key + accusative ending

The basic accusative marker is -t, but Hungarian often adds a linking vowel before it. Here that gives -ot.

Because Hungarian has two kinds of verb conjugation in many forms:

• indefinite conjugation
• definite conjugation

Here the object is definite: a kulcsot = the key.
When the verb has a definite direct object, Hungarian normally uses the definite conjugation.

So:

• hagyok = I leave / I am leaving (something indefinite, or no object stated)
• hagyom = I leave it / the specific thing

That is why hagyom is the correct form here.

Hungarian uses the definite article more often than English in this kind of expression.

So a recepción is natural Hungarian for at the reception / at reception.

In this sentence, both nouns are treated as definite:

• a kulcsot = the key
• a recepción = at the reception

English can sometimes omit the, but Hungarian usually does not here.

Recepción is recepció + -n.

That -n is a location ending often translated as on or at, and in expressions like this it is idiomatic for places such as desks, counters, or service points.

So:

• a recepción = at the reception desk / with reception
• a recepcióban = in the reception area, inside the reception space

In this sentence, the meaning is more like leaving the key at reception rather than physically inside the reception room, so a recepción fits better.

Mielőtt is a conjunction meaning before.

It introduces a full subordinate clause:

• mielőtt elmegyek = before I leave

So the structure is:

• main clause: A kulcsot a recepción hagyom
• subordinate clause: mielőtt elmegyek

Also, Hungarian normally uses a comma with this kind of clause, which is why there is a comma before mielőtt here.

Because el- is a verbal prefix attached to megyek.

• megyek = I go
• elmegyek = I go away / I leave

In a neutral sentence, the prefix usually stays attached to the verb, so elmegyek is written as one word.

These prefixes can separate in some situations, especially with negation or focus:

• Nem megyek el. = I am not leaving.

But in your sentence, elmegyek as one word is the normal form.

Hungarian often uses the present tense for future meaning when the context already makes the time clear.

Here, the meaning is understood from the situation:

• hagyom = I leave / I’ll leave
• elmegyek = I leave / I’ll go away

Because the sentence clearly refers to what happens before departing, Hungarian does not need a special future form here.

Yes. Hungarian word order is flexible, and it often reflects topic and emphasis rather than a fixed English-style pattern.

Starting with A kulcsot makes the key the main thing being talked about. The sentence then says where that key will be left.

Other orders are also possible, for example:

• Mielőtt elmegyek, a kulcsot a recepción hagyom.
• A recepción hagyom a kulcsot, mielőtt elmegyek.

These versions are similar in meaning, but they shift the emphasis slightly. So the given order is natural, but not the only possible one.