Мне неуютно в тёмной комнате.

Because this is an impersonal construction in Russian.

Russian often expresses feelings and states with:

• dative pronoun/person
  • state word

So:

• мне неуютно = I feel uncomfortable / uneasy
• literally, something like to me it is uncomfortable

That is why Russian uses мне (the dative form of я) rather than я.

Compare:

• Я устал. = I am tired.
• Мне холодно. = I am cold. / literally To me it is cold.
• Мне неуютно. = I feel uneasy / uncomfortable.

Yes, but that is normal in Russian.

In the present tense, Russian usually omits the verb to be (быть). So the sentence does not need a word for am / is / are.

• Мне неуютно в тёмной комнате. = I feel uncomfortable in a dark room.

You can think of it as:

• Мне [есть] неуютно в тёмной комнате, but есть is not actually said.

This is very common:

• Мне хорошо. = I feel good.
• Ему скучно. = He is bored.
• Нам трудно. = It is hard for us.

Неуютно comes from уют = comfort, coziness.

So неуютно means:

• not cozy
• uncomfortable
• uneasy
• not at ease

In this sentence, it usually suggests an emotional or atmosphere-based discomfort, not necessarily physical pain.

For example:

• Мне неуютно в тёмной комнате. = I feel uneasy in a dark room.
• Мне неуютно в новой компании. = I feel uncomfortable in a new group of people.

It is different from:

• неудобно = uncomfortable/inconvenient, often more physical or practical
• страшно = scary / I am afraid

So неуютно is often about the feeling of the environment.

It is the prepositional case because в here means in and shows location.

The phrase answers the question:

• Где? = Where?

So:

• в комнате = in the room
• в тёмной комнате = in the dark room

This is why:

• комната becomes комнате
• тёмная becomes тёмной

A useful contrast:

• в комнате = in the room → location → prepositional
• в комнату = into the room → direction/motion → accusative

Because adjectives must agree with the noun they describe in gender, number, and case.

The dictionary form is:

• тёмная комната = a dark room

But after в meaning in, the noun is in the prepositional singular, so the adjective changes too:

• тёмная → тёмной
• комната → комнате

So:

• nominative: тёмная комната
• prepositional: в тёмной комнате

This agreement is a basic rule in Russian.

Because комната is a feminine noun ending in -а, and in the prepositional singular it normally changes like this:

• комната → в комнате

More examples:

• школа → в школе
• машина → в машине
• книга → в книге

So в тёмной комнате is exactly what you would expect from a feminine noun in the prepositional case.

Yes. Russian word order is more flexible than English.

The neutral order here is:

• Мне неуютно в тёмной комнате.

But you could also say:

• В тёмной комнате мне неуютно.

This version puts more focus on in a dark room.

In general:

• earlier in the sentence = often topic/background
• later in the sentence = often new or emphasized information

Both are grammatical. The difference is mostly in focus and style, not basic meaning.

Yes, absolutely.

• Мне неуютно в тёмной комнате is shorter and very natural.
• Я чувствую себя неуютно в тёмной комнате is also correct, but a bit more explicit: I feel uncomfortable in a dark room.

The shorter impersonal version is extremely common in Russian and often sounds more natural in everyday speech.

Compare:

• Мне грустно. = I feel sad.
• Я чувствую себя грустно. = possible, but less idiomatic in many situations.

So for this kind of feeling/state, Russian often prefers the dative + state word pattern.

Yes. The letter ё in тёмной is pronounced yo, and it is always stressed.

So:

• тёмной sounds roughly like TYOM-noy

This matters because е and ё are different letters:

• темной is often written instead of тёмной in ordinary texts, because Russian sometimes omits the dots
• but the intended pronunciation is still usually тёмной

So when learning, it is helpful to remember the full spelling:

• тёмный
• тёмная
• тёмной

Usually it means a feeling of unease, not necessarily fear.

So:

• Мне неуютно в тёмной комнате = I do not feel comfortable in a dark room / I feel uneasy in a dark room

It does not automatically mean:

• the room is physically uncomfortable
• I am frightened

If you want to stress fear, Russian would more likely use:

• Мне страшно в тёмной комнате. = I am scared in a dark room.

If you want practical or physical discomfort, you might use:

• Мне неудобно in some contexts

So неуютно is often about the atmosphere making you feel not at ease.