Когда идёт дождь, я спускаюсь в переход и иду к метро.

This is a very common Russian expression. Идёт дождь literally looks like the rain is going, but idiomatically it means it is raining.

Russian often uses verbs of motion in weather expressions:

• идёт дождь — it is raining
• идёт снег — it is snowing

So this is not about rain physically walking somewhere; it is just the normal Russian way to describe rainfall.

Когда here means when in the sense of whenever or at times when.

So:

• Когда идёт дождь... = When/Whenever it rains...

If you used если, the meaning would shift toward if:

• Если идёт дождь... = If it is raining...

Both can be possible in some contexts, but когда is natural here because the sentence describes a habitual situation: whenever it rains, I do this.

Russian often uses the present tense to describe a repeated or habitual action, just like English can do:

• When it rains, I go down into the underpass and walk toward the metro.

So this is not necessarily happening right now. It can mean a general routine.

Also, the verbs are imperfective, which fits repeated or ongoing actions:

• идёт — is falling / rains
• спускаюсь — I go down / I descend
• иду — I go / I walk

Спускаться / спуститься is the normal verb meaning to go down, descend.

The -ся ending is part of the verb itself here. It is not really translated as a separate myself in English. So:

• спускаюсь = I go down / I descend

Without -ся, спускать usually means to lower something, let something down, release something downward:

• Я спускаю сумку. — I lower the bag.

So in your sentence, спускаюсь is correct because the subject is going down, not lowering some object.

Because this sentence describes motion into a place.

After в, Russian uses:

• accusative for motion into
• prepositional for location in

So:

• в переход — into the underpass
• в переходе — in the underpass

Since the speaker is descending into it, в переход is the correct form.

Here переход usually means an underground pedestrian passage or underpass, very often the kind you use to cross a road or to reach a metro entrance.

In cities in Russia, this is a very common word in everyday life.

Depending on context, переход can mean other kinds of crossing or transition, but in this sentence it most naturally means an underpass.

Because к means toward / to a destination, while в means into.

So:

• иду к метро — I am going toward the metro / to the metro entrance or station area
• иду в метро — I am going into the metro

In your sentence, the speaker is moving in the direction of the metro, not necessarily already entering it. That is why к метро is used.

Good question. К normally requires the dative case, but метро is one of those Russian nouns that are usually indeclinable, meaning they do not change form.

So even though the grammar requires dative, the word itself stays the same:

• к метро
• в метро
• из метро

This is normal for метро.

Because Когда идёт дождь is a subordinate clause, and Russian separates it from the main clause with a comma.

Structure:

• Когда идёт дождь, — when it rains
• я спускаюсь в переход и иду к метро. — I go down into the underpass and walk toward the metro

This is very similar to English punctuation when a when-clause comes first.

Yes. Russian word order is more flexible than English word order.

The sentence could be rearranged in some ways without changing the basic meaning, for example:

• Когда идёт дождь, я иду к метро и спускаюсь в переход.
• Я спускаюсь в переход и иду к метро, когда идёт дождь.

But the original order sounds natural because it presents the situation first, then the sequence of actions.

Russian word order often changes for emphasis, rhythm, or what information is new versus already known.

Because they describe different kinds of movement.

• спускаюсь = I go down / descend
• иду = I go / walk

So the sentence breaks the movement into two parts:

1. I go down into the underpass.
2. I walk toward the metro.

Russian often uses specific motion verbs rather than one general verb for everything.

This is about Russian verbs of motion.

• идти / иду = to go in one direction, at a particular time or in a particular movement
• ходить / хожу = to go habitually, repeatedly, or in various directions

In this sentence, even though the whole sentence describes a usual situation, each individual event is a single directed movement: when it rains, I head toward the metro. That is why иду sounds natural.

If you said хожу к метро, it would suggest something more like repeated going there in general, not this specific directed movement within the situation.

It can absolutely mean when it is raining in a general, repeated sense.

Russian present tense often covers both:

• what is happening now
• what regularly happens

So Когда идёт дождь, я спускаюсь в переход и иду к метро is best understood as a general pattern:

• Whenever it rains, I go down into the underpass and head for the metro.