Það eru aðeins tveir dagar síðan húsvörðurinn hreinsaði stigaganginn.

Because the real subject is tveir dagar (two days), which is plural, so the verb agrees with it: eru.

In Icelandic, það here is a dummy subject, similar to there or it in English. A very literal structure is:

• Það eru tveir dagar... = There are two days...

But in natural English, this becomes something like It has been two days...

So the plural eru is used because dagar is plural.

Það is not referring to a specific thing. It is just filling the subject position, much like English it in:

• It is raining
• It has been two days

This kind of það is very common in Icelandic with weather, existence, time expressions, and similar patterns.

Because dagur (day) is a masculine noun, and here it is in the nominative plural.

The numeral two changes form depending on gender and case:

• masculine: tveir
• feminine: tvær
• neuter: tvö

Since dagar is masculine plural nominative, the correct form is tveir.

It is the grammatical subject of the clause after the dummy það.

In Það eru aðeins tveir dagar..., the thing that the verb eru agrees with is tveir dagar, so it stays in the nominative.

Aðeins means only, just, or no more than.

So:

• aðeins tveir dagar = only two days

Its placement is natural here because it modifies the time phrase. Icelandic word order is somewhat flexible, but this position is very common and neutral.

Here síðan means since in the sense of since the time when.

The pattern is:

• Það eru X síðan + past tense clause

This means:

• It has been X since...

So:

• Það eru aðeins tveir dagar síðan húsvörðurinn hreinsaði stigaganginn
• It has only been two days since the caretaker cleaned the stairwell

This is a very common Icelandic structure.

Because it refers to the earlier completed action: the caretaker cleaned the stairwell, and now two days have passed since that event.

In the pattern Það eru X síðan..., the clause after síðan usually contains a past tense verb if it refers to a completed past action.

Icelandic often uses the present tense of vera (to be) in this kind of time-elapsed expression:

• Það eru tveir dagar síðan...

English uses has been, but Icelandic does not need a separate perfect form here. The meaning of elapsed time is carried by the whole construction, especially síðan plus the time expression.

So you should think of the whole pattern as an idiom:

• Það eru X síðan... = It has been X since...

The ending -inn is the suffixed definite article, meaning the.

So:

• húsvörður = caretaker / janitor / building supervisor
• húsvörðurinn = the caretaker

Icelandic usually attaches the to the end of the noun instead of using a separate word.

Because it is the direct object of hreinsaði (cleaned), so it is in the accusative case.

The base form is:

• stigagangur = stairwell / stairway / apartment hallway

The accusative singular definite form is:

• stigaganginn = the stairwell

So the sentence uses:

• hreinsaði stigaganginn = cleaned the stairwell

There are two clues:

1. Verb meaning

   • With hreinsa (to clean), the person doing the cleaning is the subject, and the thing cleaned is the object.

2. Case endings

   • húsvörðurinn is nominative singular definite
   • stigaganginn is accusative singular definite

So Icelandic marks the roles partly through case, not just word order.

Yes, but the meaning and structure are slightly different.

• Húsvörðurinn hreinsaði stigaganginn fyrir tveimur dögum síðan = The caretaker cleaned the stairwell two days ago
• Það eru aðeins tveir dagar síðan húsvörðurinn hreinsaði stigaganginn = It has only been two days since the caretaker cleaned the stairwell

These are very close in meaning, but the first focuses on when the action happened, while the second focuses on how little time has passed since it happened.

No. Síðan can have a few related uses.

Common ones include:

• since
• after that / then
• in some contexts, part of expressions like ago

In this sentence, it is a conjunction introducing the clause húsvörðurinn hreinsaði stigaganginn.

So here it specifically means since.

To some extent, yes, but the original order is very natural and neutral.

For example, Icelandic often allows emphasis by moving elements around, but:

• Það eru aðeins tveir dagar síðan...

is the most straightforward version.

If you change the order, the sentence may sound more marked or literary. For learners, it is best to remember this pattern as a chunk.

They are similar, and both can often mean only or just, but aðeins is usually a bit more neutral or formal in tone.

So:

• aðeins tveir dagar = only two days
• bara tveir dagar = just/only two days

Both are possible in many contexts, but aðeins fits very naturally in this sentence.

A very useful pattern is:

• Það eru/er + time expression + síðan + past clause

Examples:

• Það er vika síðan ég kom heim.
  It has been a week since I came home.

• Það eru þrír mánuðir síðan hún flutti.
  It has been three months since she moved.

• Það eru aðeins tveir dagar síðan húsvörðurinn hreinsaði stigaganginn.
  It has only been two days since the caretaker cleaned the stairwell.

This is one of the most important things to take away from the sentence.