Квест-комната открыта, и обратный отсчёт уже начался.

This is a compound noun. In modern Russian, especially with borrowed words, you often see structures like this with a hyphen:

• квест-комната = escape room / quest room
• бизнес-центр
• интернет-магазин

The second word is usually the main noun, and the first word specifies the type. Here, комната is the main word, so the whole phrase behaves grammatically like комната.

Because комната is feminine, the predicate also appears in the feminine form: открыта.

Открыта is the short form of открытая.

Russian often uses:

• long form adjectives for describing a noun directly
  
  • открытая комната = an open room
• short form adjectives for saying what something is right now
  
  • комната открыта = the room is open

So here:

• Квест-комната открыта = The escape room is open

This is very natural in Russian. Compare:

• Дверь закрыта = The door is closed
• Магазин открыт = The shop is open

Because it agrees with комната, which is feminine singular.

The short-form adjective changes for gender:

• masculine: открыт
• feminine: открыта
• neuter: открыто
• plural: открыты

Since комната is feminine, Russian uses открыта.

Not exactly. Grammatically, it is a short-form adjective (historically related to a participle), and it functions like the predicate in the sentence.

Russian often omits the verb to be in the present tense, so:

• Квест-комната открыта
  literally: Escape-room open

But in natural English, you translate it as:

• The escape room is open

So the idea of is is understood, even though there is no separate present-tense verb for to be.

Literally, обратный отсчёт means something like reverse counting:

• обратный = reverse, backward
• отсчёт = counting / count

Together, it means countdown.

This is a standard Russian expression for a countdown, such as before an event, launch, deadline, or timed game.

Because the verb here is начаться, not начать.

• начать = to begin/start something
  
  • Он начал игру = He started the game
• начаться = to begin/start by itself
  
  • Игра началась = The game started

In this sentence, обратный отсчёт is the thing that began, so Russian uses the intransitive/reflexive verb:

• обратный отсчёт начался = the countdown started

The -ся marks the verb as the reflexive form начаться.

In many cases, this reflexive form does not mean a literal reflexive action like wash oneself. Instead, it often makes the verb intransitive:

• начать что-то = to start something
• начаться = to start / to begin

So начался here simply means began / started.

Because отсчёт is masculine.

You can tell because it ends in a consonant, which is the usual pattern for masculine nouns in Russian. The past tense agrees with the gender of the subject:

• masculine: начался
• feminine: началась
• neuter: началось
• plural: начались

So:

• обратный отсчёт начался

Уже means already.

It shows that the action has happened by now, often with a sense that it may be earlier than expected or that the relevant moment has arrived:

• отсчёт уже начался = the countdown has already started

In this sentence, уже emphasizes urgency: the room is open, and the countdown is not just about to begin — it is already underway.

That is the most natural placement here. Russian word order is flexible, but not random.

• обратный отсчёт уже начался = neutral, natural
• уже обратный отсчёт начался = possible, but more marked
• обратный отсчёт начался уже = possible in context, but less neutral

Placing уже before the verb is very common when you want to say that something has already happened.

Because и is joining two full clauses:

1. Квест-комната открыта
2. обратный отсчёт уже начался

Each part has its own subject and predicate, so Russian normally uses a comma between them.

This is similar to English:

• The escape room is open, and the countdown has already started.

You could, but it means something slightly different.

• Квест-комната открыта = the escape room is open
  This describes the current state.
• Квест-комната открылась = the escape room opened / has opened
  This focuses on the event of becoming open.

So in your sentence, открыта is better if the point is the present situation rather than the moment of opening.

Russian has no articles like the or a/an.

So:

• Квест-комната can mean the escape room or an escape room
• обратный отсчёт can mean the countdown or a countdown

The context tells you which meaning is intended. In this sentence, English naturally uses the because both things are specific in the situation.

Both main nouns are in the nominative case:

• квест-комната
• обратный отсчёт

That is because they are the subjects of their clauses:

• Квест-комната открыта
• обратный отсчёт начался

The adjectives also agree accordingly:

• обратный matches отсчёт in masculine nominative singular
• открыта matches комната in feminine singular as a short-form predicate

Because the standard spelling of this word is отсчёт, with ё.

This matters because:

• ё shows the stressed sound
• it helps distinguish pronunciation clearly

In many everyday texts, Russians often write е instead of ё, so you may also see отсчет, but the correct dictionary form is отсчёт.

The pronunciation is roughly at-SCHYOT.