Sundfötin hennar þornuðu á stólnum meðan við gengum á sandinum.

Yes. Sundföt literally means swimming clothes / swimwear, and it is very commonly used in the plural in Icelandic.

So:

• sundföt = swimsuit / swimwear / bathing clothes
• sundfötin = the swimsuit / the swimwear

Even if English might use a singular idea like her swimsuit, Icelandic often uses the plural noun sundföt. That is why the verb is also plural later in the sentence.

The ending -in is the definite article attached to the noun, so sundfötin means the swimwear or her swimsuit depending on context.

In Icelandic, possessives like hennar are very often placed after the noun.

So:

• sundfötin hennar = her swimwear
• literally: the swimwear her

This is a very normal Icelandic pattern, especially with pronoun possessives:

• maðurinn minn = my husband
• bíllinn hans = his car
• húsið okkar = our house

So although it feels reversed from English, sundfötin hennar is exactly the natural Icelandic structure.

Hennar means her.

It is the possessive form used for a female owner:

• hans = his
• hennar = her

So:

• Sundfötin hennar = Her swimwear / Her swimsuit

A useful point: hennar itself does not change form here. The noun carries the definite article, and the possessive simply follows it.

Because the subject sundfötin is grammatically plural.

• sundfötin = plural
• þornuðu = past tense plural of þorna (to dry)

So Icelandic is making the verb agree with the plural subject:

• Sundfötin hennar þornuðu = Her swimwear dried

Compare:

• Bolurinn þornaði = The shirt dried
• Fötin þornuðu = The clothes dried

Even if English might use a singular translation such as her swimsuit dried, Icelandic still treats sundfötin as plural.

The base form is þorna, meaning to dry or to become dry.

In this sentence:

• þornuðu = dried
• tense: past
• subject agreement: plural

So:

• að þorna = to dry / to become dry
• þornaði = dried with a singular subject
• þornuðu = dried with a plural subject

This verb is describing a change of state, so the meaning is became dry rather than dried something.

Because this sentence describes location, not movement toward a place.

In Icelandic, á can take different cases depending on meaning:

• á + dative = on, when something is located somewhere
• á + accusative = onto, when there is movement toward the surface

Here, the clothes were already there and dried there:

• á stólnum = on the chair
  (dative, static location)

If the sentence meant onto the chair, you would expect accusative:

• á stólinn = onto the chair

So the dative in stólnum tells you this is a static location.

Because stólnum is the dative singular definite form of stóll (chair).

Here is the pattern:

• stóll = chair
• stólinn = the chair (nominative/accusative singular definite)
• stólnum = the chair (dative singular definite)

Since á here means on in a location sense, it requires the dative, so we get:

• á stólnum = on the chair

This is a very common Icelandic pattern with prepositions and case.

Meðan means while.

It introduces a subordinate clause showing that two actions happened at the same time:

• Sundfötin hennar þornuðu á stólnum = Her swimwear dried on the chair
• meðan við gengum á sandinum = while we were walking on the sand

So meðan connects the two events and shows simultaneity.

You will often see it in sentences like:

• Ég las meðan hún eldaði. = I read while she cooked.
• Þau töluðu meðan þau biðu. = They talked while they waited.

Gengum is the past tense, 1st person plural form of ganga (to walk).

So:

• að ganga = to walk
• við gengum = we walked

This is an irregular verb, so the form is not built in a completely predictable way from the infinitive.

In the sentence:

• meðan við gengum á sandinum = while we walked on the sand

English might also translate this more naturally as while we were walking on the sand, even though Icelandic simply uses the past form gengum.

For the same reason as á stólnum: it describes location.

• sandur = sand
• sandinum = the sand in the dative singular definite

So:

• á sandinum = on the sand

Because the meaning is walking on the sand as a location/surface, á takes the dative here.

If you are learning Icelandic cases, this sentence is a good example of á + dative used twice for static location/surface:

• á stólnum = on the chair
• á sandinum = on the sand

It is actually fairly close to English here.

The basic structure is:

• Sundfötin hennar = subject
• þornuðu = verb
• á stólnum = prepositional phrase
• meðan við gengum á sandinum = subordinate clause

So the sentence is basically:

• Her swimwear dried on the chair while we walked on the sand.

That said, one very Icelandic feature is the noun phrase:

• sundfötin hennar rather than English her swimwear

So the overall clause order is familiar, but some internal grammar—especially possession and case—is distinctly Icelandic.

Yes, depending on context, that can be a natural English translation.

The Icelandic past tense here does not force a single English choice. Depending on context, you might translate it as:

• Her swimwear dried on the chair while we walked on the sand.
• Her swimsuit was drying on the chair while we were walking on the sand.
• Her bathing suit dried on the chair while we were walking on the sand.

So even though the Icelandic verb forms are simple past, English may choose either simple past or past progressive to sound natural.

All three can work, depending on context.

Most literally, sundföt is something like swimming clothes / swimwear. But in natural translation, English often prefers:

• her swimsuit
• her bathing suit
• her swimwear

The best choice depends on what the speaker means:

• one item of beachwear: her swimsuit
• a more general or neutral meaning: her swimwear
• American English style: her bathing suit

So the Icelandic wording is a little broader than a single fixed English equivalent.