Við vitum ekki hvert strætóinn fer héðan.

Because hvert means to where / where to, while hvar means where in the sense of location.

Icelandic often makes a three-way distinction:

• hvar = where, at what place
• hvaðan = from where
• hvert = to where

In this sentence, the bus is going somewhere, so Icelandic uses hvert.

That is also why the sentence can contain both:

• hvert = where the bus is going to
• héðan = from here

So the structure is basically: We don’t know to where the bus goes from here.

Strætóinn means the bus.

The base word is strætó = bus.
The ending -inn is the suffixed definite article, so Icelandic usually says the bus by attaching the article to the noun instead of putting a separate word before it.

So:

• strætó = a bus / bus
• strætóinn = the bus

This is very common in Icelandic:

• bíll = car
• bíllinn = the car

Because this is an embedded question, not a direct question.

Compare:

• Direct question: Hvert fer strætóinn? = Where is the bus going?
• Embedded question: Við vitum ekki hvert strætóinn fer. = We don’t know where the bus is going.

In embedded questions, Icelandic normally does not use the same inverted order as direct questions. After the question word, you usually get more regular clause order:

• hvert strætóinn fer

So an English speaker can think of it like this:

• direct question: question-word + verb + subject
• embedded question: question-word + subject + verb

This follows normal Icelandic main-clause word order.

In a main clause, the finite verb usually comes early, and ekki often comes right after it unless something else changes the structure.

So here:

• Við = subject
• vitum = finite verb
• ekki = not

That gives:

• Við vitum ekki ...

This is very natural Icelandic word order.

Vitum is the 1st person plural present form of vita, which means to know.

So:

• ég veit = I know
• við vitum = we know

Because the subject is við = we, the verb appears as vitum.

Fer is the 3rd person singular present form of fara, meaning to go, to travel, or for vehicles often to go / run.

So here:

• strætóinn = the bus
• fer = goes

Because strætóinn is singular, the verb is singular too.

A useful comparison:

• strætóinn fer = the bus goes
• strætóarnir fara = the buses go

Héðan means from here.

It is one of a set of place/direction words that English often does not distinguish as clearly as Icelandic does:

• hér / hérna = here
• hingað = to here
• héðan = from here

So fer héðan means goes from here or leaves from here.

Normally, no. Icelandic usually keeps the subject pronoun.

Even though vitum clearly means we know, Icelandic is generally not a language where you regularly drop subject pronouns the way some other languages do.

So the natural full sentence is:

• Við vitum ekki ...

Leaving out við would usually sound incomplete or unnatural in an ordinary sentence.

Yes, it is related historically, but in this sentence you should learn hvert as a separate question word meaning to where / where to.

This can be confusing because hver-words cover several meanings in Icelandic, such as who, which, and certain directional forms. But here, hvert is not functioning like which. It is the normal interrogative word for destination.

So in this sentence, the safest interpretation is simply:

• hvert = where to

Normally no, not in standard Icelandic.

That word order would look like a direct question order inside an embedded clause, and that is not what Icelandic normally does here.

The correct embedded structure is:

• Við vitum ekki hvert strætóinn fer héðan.

But the direct question is:

• Hvert fer strætóinn héðan?

So the difference is important:

• direct question: hvert fer strætóinn
• embedded question: hvert strætóinn fer

Yes, very often that is the natural way to understand it.

Literally, fer héðan is goes from here, but with a bus, English often prefers leaves from here or departs from here.

So even though the basic verb is fara = go, the real-life meaning in context can be closer to:

• leave
• depart
• go from here

That is very normal when the subject is a vehicle or form of transport.