Gegnt leikvellinum er lítil búð þar sem ég kaupi stundum vatn.

Here gegnt means opposite, across from, or facing.

In this sentence it is used with the dative case, so the noun after it appears in dative:

• leikvellinum = the playground in the dative singular

So gegnt leikvellinum means opposite the playground.

Because leikvöllur is the basic dictionary form, the nominative singular.

After gegnt, Icelandic uses the dative, so the noun changes form:

• leikvöllur = playground
• leikvellinum = to/at/by the playground, or here opposite the playground

The ending -inum shows:

• dative singular
• definite meaning the playground, not just a playground

Icelandic often puts a place expression first when it wants to set the scene.

So instead of starting with a small shop, the sentence starts with opposite the playground. That is very natural in Icelandic.

This also affects word order because Icelandic is a verb-second language in main clauses. When Gegnt leikvellinum comes first, the finite verb must come second:

• Gegnt leikvellinum er lítil búð

A more English-like order such as Lítil búð er gegnt leikvellinum is possible in some contexts, but the given version is very natural and common.

This is because of the verb-second rule.

In a main clause, the finite verb usually comes in the second position. Since Gegnt leikvellinum is placed first, er has to come next:

• 1st element: Gegnt leikvellinum
• 2nd element: er
• then the subject: lítil búð

So the order is not random; it follows a central Icelandic grammar rule.

Because the adjective lítil must agree with búð.

Búð is:

• feminine
• singular
• nominative

So lítill changes to lítil to match it.

That gives:

• lítil búð = a small shop

If the noun were masculine or neuter, or in another case, the adjective form would change.

English uses a dummy word: there is.

Icelandic does not always need that. It can simply say:

• er lítil búð = is a small shop

With the place phrase in front, the full idea becomes:

• Gegnt leikvellinum er lítil búð
• literally: Opposite the playground is a small shop
• natural English: There is a small shop opposite the playground

So Icelandic often expresses this idea without an extra word corresponding to English there.

Þar sem means where in this sentence.

It introduces a clause describing the place:

• lítil búð þar sem ég kaupi stundum vatn
• a small shop where I sometimes buy water

Literally, þar means there, and sem is a relative connector, but together þar sem very often means where.

Because the clause refers to a place.

When Icelandic wants to mean where, especially after a place noun like búð, it very often uses þar sem:

• búð þar sem... = shop where...

Using only sem is possible in some relative clauses, but þar sem is especially clear and natural when the meaning is specifically in/at which place.

Because kaupa is the infinitive: to buy.

Here the verb is conjugated for ég in the present tense:

• ég kaupi = I buy

So:

• ég kaupi stundum vatn = I sometimes buy water

Some present tense forms of Icelandic verbs are:

• ég kaupi = I buy
• þú kaupir = you buy
• hann/hún/það kaupir = he/she/it buys

Stundum means sometimes.

In this clause it comes after the verb:

• ég kaupi stundum vatn

That is a very natural position in Icelandic. Adverbs of frequency often appear after the finite verb and before the object.

So the structure is:

• ég = I
• kaupi = buy
• stundum = sometimes
• vatn = water

Here vatn is the direct object of kaupi, so it is in the accusative.

However, vatn is a neuter noun, and in the singular its nominative and accusative forms are the same:

• nominative: vatn
• accusative: vatn

So you do not see a visible change, even though the grammatical case is accusative.

Because the sentence is talking about water in a general, indefinite sense:

• I sometimes buy water

It is not the water, and it is not specifying a particular bottle already known to the listener.

So Icelandic simply uses:

• vatn = water

If it were definite, Icelandic could use the definite form:

• vatnið = the water

Yes. It is a relative clause that modifies búð.

So the structure is:

• lítil búð = a small shop
• þar sem ég kaupi stundum vatn = where I sometimes buy water

Together:

• lítil búð þar sem ég kaupi stundum vatn
• a small shop where I sometimes buy water

This clause gives extra information about which shop is meant.

No. Another very common expression is á móti.

For example:

• gegnt leikvellinum
• á móti leikvellinum

Both can mean opposite the playground or across from the playground.

Gegnt can sound a bit more formal or written in some contexts, while á móti is very common in everyday speech. Both are useful to know.