Museo avataan aikaisin aamulla, ja siellä on paljon nähtävää.

Finnish has no articles, so there is no separate word for a/an or the.

So museo can mean:

• a museum
• the museum

The context tells you which one is meant. In this sentence, it is understood as the museum.

Avataan is the present passive form of avata (to open).

So Museo avataan literally means something like:

• The museum is opened
• People open the museum
• The museum opens

In English, opening times are often expressed with opens, but Finnish very naturally uses the passive when the doer is not important or is obvious.

This is especially common in:

• schedules
• notices
• public information
• instructions

This is a very common Finnish case question.

In an active sentence, you would say:

• He avaavat museon = They open the museum

There, museon is the object.

But in a passive sentence, a total object often appears in the nominative form instead:

• Museo avataan

So even though English speakers may expect something like museon, Finnish uses museo here because of the passive construction.

Yes, but it is not exactly the same.

• Museo avataan = the museum is opened / the staff open it / it opens according to schedule
• Museo avautuu = the museum opens, with more of an intransitive sense

In practice, avataan is very natural in formal or informational language, especially when talking about opening hours. Avautuu is possible, but it gives the sentence a slightly different feel.

It has two parts:

• aikaisin = early
• aamulla = in the morning

So together:

• aikaisin aamulla = early in the morning

Aamulla is the form of aamu used for times of day. Finnish often uses this pattern:

• aamulla = in the morning
• päivällä = during the day / in the daytime
• illalla = in the evening
• yöllä = at night

Not in this sentence.

Even though aikaisin can look like a superlative form, here it is simply used as an adverb meaning early.

So:

• aikaisin aamulla = early in the morning

not

• earliest in the morning

For a learner, it is best to understand aikaisin here as a fixed everyday adverb.

Because Finnish often refers back to a place with a location word like:

• siellä = there
• täällä = here
• tuolla = over there

Since a museum is a place, siellä naturally means there / in the museum.

So:

• siellä on paljon nähtävää = there is a lot to see there / in the museum

You could also say:

• Museossa on paljon nähtävää

But siellä avoids repeating the noun and sounds very natural.

Nähtävää comes from nähdä (to see).

In this kind of sentence, it means something like:

• something to see
• things worth seeing
• seeable stuff

So:

• paljon nähtävää = a lot to see

This is a very common Finnish pattern. Similar expressions are:

• paljon tekemistä = a lot to do
• paljon syötävää = a lot to eat
• paljon luettavaa = a lot to read

You do not need to fully analyze it at first; it is very useful to learn paljon nähtävää as a chunk.

Because paljon usually takes the partitive, and here the phrase is understood in a general, uncounted way:

• a lot to see
• not many separate seeable items

So Finnish uses:

• paljon nähtävää

This is similar to how English says a lot to do rather than counting separate tasks one by one.

If you wanted to emphasize separate countable things, you would normally use a different structure, for example:

• paljon nähtäviä asioita = many things to see

Because ja connects two full clauses, and each clause has its own finite verb:

• Museo avataan aikaisin aamulla
• siellä on paljon nähtävää

In Finnish, when coordinating two independent clauses like this, a comma before ja is normal.

So the comma is there because the sentence is really:

1. The museum opens early in the morning
2. and there is a lot to see there

This is a very common Finnish structure for saying that something exists somewhere:

• [place] + on + [thing]

So:

• siellä on paljon nähtävää

literally follows the pattern:

• there is a lot to see there

This kind of word order is very natural in Finnish when introducing what is available in a place.