Kinnin hennar er rauð eftir göngutúrinn úti.

The base form is kinn, which means cheek.

Kinnin = kinn + the suffixed definite article -in, so it means the cheek.

This is very common in Icelandic: instead of using a separate word for the, Icelandic often attaches the definite article to the noun itself.

For example:

• kinn = cheek
• kinnin = the cheek

In Icelandic, possessive words like hennar often come after the noun, especially when the noun is already definite.

So:

• kinnin hennar = her cheek

This structure is very natural in Icelandic. English usually says her cheek, but Icelandic often prefers something closer to the cheek of hers in structure.

Hennar means her.

It is the possessive form used for a female owner or reference:

• bókin hennar = her book
• bíllinn hennar = her car
• kinnin hennar = her cheek

So here it shows that the cheek belongs to or is associated with her.

The adjective has to agree with the noun it describes in gender, number, and case.

The noun kinn is feminine singular, so the adjective also takes the feminine singular form:

• masculine: rauður
• feminine: rauð
• neuter: rautt

Because kinnin is feminine singular, the correct form is rauð.

Er means is.

It is the present tense of the verb að vera = to be.

So:

• hún er = she is
• kinnin hennar er rauð = her cheek is red

Because kinnin is singular here: the cheek, not the cheeks.

So the verb must also be singular:

• er = is
• eru = are

If the sentence were about both cheeks, you would need a plural noun and plural verb.

Here eftir means after.

It introduces what happened earlier in time:

• eftir göngutúrinn = after the walk

So the sentence is saying that her cheek is red after that walk.

Göngutúr means a walk or walk. Göngutúrinn means the walk.

Again, Icelandic adds the definite article to the end of the noun:

• göngutúr = walk
• göngutúrinn = the walk

So eftir göngutúrinn means after the walk.

Here eftir takes the accusative because it means after in a temporal sense.

So göngutúrinn is in the accusative singular definite form.

This is something learners often have to memorize with prepositions: Icelandic prepositions can require different cases depending on meaning.

Úti means outside or outdoors.

In this sentence, it adds the idea that the walk took place outside:

• göngutúrinn úti = the walk outside / the walk outdoors

It is very natural in Icelandic for an adverb like úti to come near the end of the sentence.

No. Here úti is an adverb, not a preposition.

It describes location or setting:

• Hann er úti. = He is outside.
• Við borðuðum úti. = We ate outside.

In your sentence, it tells you the walk happened outdoors.

Because the sentence refers to specific things:

• kinnin hennar = her cheek, a specific cheek
• göngutúrinn = the walk, a specific walk already understood from context

Icelandic often uses the definite form where English also uses the, but the article is attached to the noun.

It means one cheek, because it is singular.

If you wanted to talk about both cheeks, you would use a plural form instead.

So this sentence focuses on a single cheek being red.

Yes, that is a very natural way to understand it.

The combination eftir göngutúrinn úti suggests that being outdoors on the walk is what caused the redness.

So the idea is not just sequence in time, but also a likely cause:

• after the outdoor walk
• because of the outdoor walk

It is very normal.

The basic structure is:

• Kinnin hennar = subject
• er = verb
• rauð = complement
• eftir göngutúrinn úti = adverbial phrase

So the sentence follows a straightforward pattern: subject + verb + adjective + time/circumstance phrase

You might see possessives before nouns in some contexts, but kinnin hennar is the more natural structure here.

Also, hennar kinn without the definite ending sounds less natural in ordinary usage for this sentence. Icelandic very often prefers:

• nafn hennar = her name
• húsið hennar = her house
• kinnin hennar = her cheek

So for a learner, noun + definite article + hennar is the safest pattern to remember here.