Kiedy pada deszcz, wolę iść przez tunel niż przez most.

Polish often expresses weather with a verb plus a noun.

• pada = falls / is falling
• deszcz = rain

So pada deszcz literally feels like rain is falling.

This is a very normal Polish way to talk about weather:

• Pada śnieg = It’s snowing
• Pada on its own can also mean It’s raining, if the context is clear.

So even though English uses it rains, Polish usually says something closer to rain falls.

Both word orders are possible in Polish, but kiedy pada deszcz is the more neutral, natural order here.

Polish word order is more flexible than English, but it is not random. The version in the sentence sounds like a standard statement:

• kiedy pada deszcz = when it rains

If you say kiedy deszcz pada, it may sound more marked, poetic, or contrastive depending on context.

So for a learner, the safest default is:

• verb + noun in this weather expression: pada deszcz

Here kiedy means when.

Yes, gdy is also possible:

• Kiedy pada deszcz, wolę iść przez tunel...
• Gdy pada deszcz, wolę iść przez tunel...

Both mean basically the same thing.
A few small notes:

• kiedy is very common in everyday speech
• gdy can sound a little more formal or literary in some contexts
• in many sentences, they are interchangeable

So as a beginner, kiedy is a very safe choice.

Because kiedy pada deszcz is a subordinate clause.

Polish punctuation usually separates this kind of clause with a comma:

• Kiedy pada deszcz, wolę iść przez tunel niż przez most.

This is similar to English:

• When it rains, I prefer to go through the tunnel rather than over the bridge.

In Polish, commas with subordinate clauses are generally more strictly required than in English.

Wolę is the 1st person singular form of the verb woleć = to prefer.

So:

• woleć = to prefer
• wolę = I prefer

Examples:

• Wolę kawę. = I prefer coffee.
• Wolę zostać w domu. = I prefer to stay home.

In your sentence:

• wolę iść = I prefer to go / walk

It is not the same as:

• chcę iść = I want to go
• lubię iść = I like going

So wolę expresses preference between options.

Iść usually means to go on foot in one direction, so it often translates as to go or to walk, depending on the English sentence.

In this context:

• wolę iść przez tunel = I prefer to go through the tunnel

English may not always mention on foot, but Polish often makes that distinction more clearly.

Compare:

• iść = to go/walk on foot
• jechać = to go by vehicle
• chodzić = to walk/go regularly, repeatedly, or in general

So iść fits well if the speaker means a single trip on foot.

In standard Polish, repeating przez is the natural and correct choice here:

• przez tunel niż przez most

This makes the comparison clear and balanced:

• through the tunnel
• rather than across the bridge

Leaving out the second przez would sound incomplete or unnatural in this sentence.

Polish often repeats prepositions where English sometimes would too:

• do szkoły i do pracy
• na stole i na krześle

So here, repeating przez is exactly what you should expect.

After przez, Polish uses the accusative case.

So:

• przez tunel
• przez most

These are accusative forms.

Why do they look the same as the dictionary form?
Because tunel and most are masculine inanimate nouns, and for many masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

Compare:

• nominative: tunel

• accusative: tunel

• nominative: most
• accusative: most

But with some other nouns, you would see a visible change:

• mam kota (accusative of kot)

So the case is accusative, even though the form does not change here.

Niż means than in comparisons.

Here it connects two options after wolę:

• wolę iść przez tunel niż przez most
• literally: I prefer to go through the tunnel than through the bridge
• natural English: I prefer to go through the tunnel rather than over the bridge

In Polish, niż is commonly used after comparative ideas such as:

• lepiej niż = better than
• bardziej niż = more than
• wolę ... niż ... = I prefer ... to / rather than ...

So this is a very useful pattern:

• Wolę herbatę niż kawę.
• Wolę zostać w domu niż wychodzić.

Not naturally in this sentence.

With woleć, Polish normally uses:

• wolę X niż Y

For example:

• Wolę kawę niż herbatę.
• Wolę iść przez tunel niż przez most.

You may also hear wolę X od Y, especially with nouns:

• Wolę kawę od herbaty.

But in your sentence, where you are comparing full phrases with a preposition, niż is the clearer and more standard choice:

• wolę iść przez tunel niż przez most

So for learners, the best rule is:

• use niż after wolę unless you are very comfortable with other structures

Because Polish has no articles.

English uses:

• the tunnel
• a tunnel
• the bridge
• a bridge

Polish simply says:

• tunel
• most

Whether it means a or the depends on context.

So:

• przez tunel can mean through a tunnel or through the tunnel
• przez most can mean across a bridge or across the bridge

This is one of the big differences between English and Polish.

Yes, Polish word order is fairly flexible, but different versions can sound more or less natural depending on emphasis.

The original sentence is very natural:

• Kiedy pada deszcz, wolę iść przez tunel niż przez most.

You could also say:

• Wolę iść przez tunel niż przez most, kiedy pada deszcz.

This is still understandable, but it puts the main statement first and the time condition later.

The original version is probably the best neutral choice because it clearly sets up the condition first:

• When it rains, ...

So yes, word order can change, but the original is excellent standard Polish.

Yes. Pada is from the imperfective verb padać.

Imperfective is used here because the sentence describes a general situation or repeated condition:

• When it rains, I prefer...

It is not about one single completed action. It is about what usually happens or what the speaker prefers in that situation.

So:

• padać = imperfective, ongoing/repeated weather event
• pada = it is raining / it rains

This is exactly the form you would expect in a general statement like this one.

Yes, in Polish most means bridge.

It is a normal, everyday word:

• Most jest zamknięty. = The bridge is closed.
• Idziemy przez most. = We’re going across the bridge.

Even if you know another Slavic language where a similar word means something else, in Polish most is simply bridge.