Odemkli jsme truhlu, aniž bychom rozluštili kód.

Czech past tense is usually built from:

• a past participle: odemkli
• plus a form of to be: jsme

So:

• odemkl jsem = I unlocked
• odemkli jsme = we unlocked

The ending -li shows a masculine animate or mixed-gender plural subject. In practice, with we, this form is very common unless the group is entirely feminine, in which case you could get odemkly jsme.

Because it is the direct object of the verb odemknout.

The basic form is:

• truhla = chest, trunk

But after a transitive verb like unlock, Czech uses the accusative case:

• truhlu = the chest/trunk as the thing being unlocked

This is a normal pattern for feminine nouns ending in -a:

• žena → ženu
• kniha → knihu
• truhla → truhlu

Aniž means something like:

• without
• without ...ing
• without the fact that ...
• without having ...

In this sentence, it introduces an action that did not happen, even though the main action did:

• Odemkli jsme truhlu, aniž bychom rozluštili kód.
• We unlocked the chest without deciphering the code.

It is a conjunction, not a preposition, so it introduces a whole clause.

That is one of the standard Czech patterns:

• aniž + conditional

So after aniž, Czech often uses forms like:

• bych
• bys
• by
• bychom
• byste

Here:

• bychom = we would

But in this construction, it usually does not really mean normal English would. It is just the standard grammar after aniž.

So:

• aniž bychom rozluštili kód
  = without deciphering the code

A very literal translation would sound odd in English, something like without our having deciphered the code.

Because the second clause is not a normal past-tense statement. It is part of the fixed construction:

• aniž + conditional

So Czech does not say:

• aniž jsme rozluštili kód in this meaning

Instead it says:

• aniž bychom rozluštili kód

This is one of those patterns you mainly have to learn as a unit.

It looks similar to a past form, but here it is part of the conditional construction.

The Czech conditional is built with:

• bych/bychom/...
• plus the l-participle

So:

• bychom rozluštili = we would decipher / we would have deciphered

After aniž, this combination means roughly:

• without deciphering
• without having deciphered

So yes, rozluštili is the same participle shape you also see in the past tense, but here it is functioning inside the conditional.

Because kód is masculine inanimate, and in the singular its nominative and accusative are often the same.

So:

• kód = code
• rozluštit kód = to decipher the code

This is very common with masculine inanimate nouns:

• hrad → vidím hrad
• stůl → mám stůl
• kód → rozluštit kód

So the object is in the accusative, but it happens to look identical to the dictionary form.

Because the sentence talks about completed whole actions.

• odemknout = to unlock completely, successfully
• rozluštit = to decipher/solve completely

The main event is clearly completed:

• we unlocked the chest

And the second action is presented as a completed action that did not happen:

• we did not decipher the code

Perfective aspect fits that meaning well.

If you used imperfective verbs, the sentence would sound different, focusing more on process or repeated action.

Yes, but the structure changes.

You could say things like:

• Odemkli jsme truhlu bez rozluštění kódu.
• Odemkli jsme truhlu bez toho, abychom rozluštili kód.

These are similar in meaning, but not identical in style.

• aniž bychom rozluštili kód sounds very natural and elegant
• bez rozluštění kódu is more condensed and noun-based
• bez toho, abychom... is also common and often feels slightly more conversational or explanatory

So aniž is not the only option, but it is a very standard one.

It is standard Czech and completely correct. It often feels a bit more:

• written
• polished
• formal-ish

than some simpler alternatives.

In everyday speech, people might sometimes prefer:

• bez toho, abychom rozluštili kód

But aniž bychom is still very normal and useful, especially in written Czech and careful speech.

Because Czech usually does not need subject pronouns unless they are emphasized.

The forms already show the subject:

• odemkli jsme = we unlocked
• bychom rozluštili = we would decipher / we deciphered in this construction

So adding my would only be needed for emphasis or contrast:

• My jsme truhlu odemkli... = We were the ones who unlocked the chest...

Normally, Czech just leaves the pronoun out.

Yes. Czech word order is flexible.

For example, you could also say:

• Aniž bychom rozluštili kód, odemkli jsme truhlu.

That means the same thing.

The original order is very natural because it gives:

1. the main event first
2. then the without ...ing part

The comma is important because aniž introduces a subordinate clause.

In Czech, short forms like jsem, jsi, jsme, jste, bychom behave like clitics, which tend to stand near the beginning of their clause, often in the second position.

So:

• Odemkli jsme truhlu...

is the normal order.

You usually would not say:

• Jsme odemkli truhlu...

except in very marked or unusual contexts.

This is a common Czech word-order rule that learners gradually get used to.

Yes, potentially.

The plural participle changes according to gender:

• -li for masculine animate or mixed groups
• -ly for all-feminine groups

So if the speakers were all women, you might expect:

• Odemkly jsme truhlu, aniž bychom rozluštily kód.

In practice, learners usually first meet the -li version, which is often used as the default example. But the feminine plural forms do exist and matter.

The dictionary forms are:

• odemknout = to unlock
• rozluštit = to decipher, crack, solve

The sentence uses their finite forms:

• odemkli jsme from odemknout
• rozluštili in the aniž bychom construction from rozluštit

It is useful to learn both dictionary forms together with their aspectual partners if possible:

• odemknout / odemykat
• rozluštit / rozlušťovat

That helps you understand why these perfective forms were chosen here.