kannai ha sizuka desu.

It is read:

かんない は しずか です
Romanized: kannai wa shizuka desu

A very important point: the particle は is written ha, but when it is used as a topic particle, it is pronounced wa.

So you say:

kannai wa shizuka desu

は marks the topic of the sentence.

So 館内は means something like:

• as for the inside of the building/facility
• inside the building, ...

The rest of the sentence, 静かです, says something about that topic.

So the structure is:

• 館内は = topic
• 静かです = comment about the topic

This topic-comment structure is extremely common in Japanese.

This is just a special pronunciation rule for the particle は.

• As a normal syllable in a word, は is usually read ha
• As the topic particle, it is pronounced wa

For example:

• はな = hana = flower
• 私は = watashi wa = as for me

So in 館内は静かです, the は is a particle, so it is pronounced wa.

静か is a na-adjective.

In Japanese, there are two major adjective types learners usually meet early on:

• i-adjectives like 高い
• na-adjectives like 静か

That is why 静か behaves differently from an i-adjective.

Here, 静かです means is quiet in polite style.

Because な is only used when a na-adjective comes before a noun.

Examples:

• 静かな部屋 = a quiet room
• 静かな館内 = a quiet building interior

But when the adjective is at the end of the sentence, you do not use な:

• 館内は静かです = The building interior is quiet

So:

• before a noun: 静かな + noun
• at the end of a sentence: 静かです / 静かだ

Not exactly.

In beginner translations, です is often treated like is, and that is useful. But grammatically, it does not always match English perfectly.

In this sentence, です mainly makes the sentence polite.

Compare:

• 館内は静かです = polite
• 館内は静かだ = plain
• 館内は静か = very casual/plain, depending on context

So です is not simply a direct one-word equivalent of is in every situation. It is better to think of 静かです as a polite way to state quiet as a predicate.

館内 means inside a building/facility or within the premises.

It is a somewhat formal or institutional word, often seen in places like:

• museums
• libraries
• public buildings
• event halls
• department stores

You may see it in announcements such as:

• 館内ではお静かにお願いします = Please be quiet inside the building
• 館内案内 = facility guide / information for inside the building

So 館内 is not just any casual inside. It specifically refers to the inside area of a building or facility.

Japanese often leaves out things that are clear from context.

In English, you might say:

• It is quiet inside the building
• The building interior is quiet

Japanese does not need a dummy subject like it. If the topic is already given, the sentence can simply be:

館内は静かです

That is completely natural in Japanese.

You sometimes can, but the nuance changes.

• 館内は静かです = as for inside the building, it is quiet
• 館内が静かです = the inside of the building is what is quiet / the inside is quiet (with more focus on 館内)

In many beginner contexts, は is the more natural choice because it presents 館内 as the topic.

Using が can sound more specific or contrastive depending on context, such as when answering a question like:

• どこが静かですか。 = What place is quiet?
• 館内が静かです。 = The inside of the building is quiet.

So は is usually the safer choice here unless you specifically want focus.

Yes.

Polite:

• 館内は静かです

Plain:

• 館内は静かだ

In casual conversation, people may also say:

• 館内は静か

That last version is less formal and depends on context and speaking style.

So if you are speaking politely to strangers, customers, teachers, or in formal settings, です is the right choice.

The basic structure is:

[topic] + [description]

So:

• 館内は = topic
• 静かです = description

Japanese often puts the topic first and then gives information about it.

A very literal breakdown is:

• As for the building interior, [it] is quiet.

This is a very common and useful sentence pattern:

• 今日は暑いです = As for today, it is hot
• この部屋はきれいです = As for this room, it is clean
• 館内は静かです = As for inside the building, it is quiet

Japanese is normally written without spaces, so the sentence would usually appear as:

館内は静かです。

Learner materials often add spaces to make the structure easier to see:

館内　は　静か　です。

That spacing is just for study purposes. In real Japanese text, you normally will not see those spaces.