Die Boulderhalle öffnet um zehn.

Die is the definite article the for the noun Boulderhalle.

Here, Boulderhalle is a feminine noun, so in the nominative singular it takes die:

• die Boulderhalle = the bouldering gym

So Die Boulderhalle is the subject of the sentence.

Boulderhalle is a compound noun:

• Boulder = bouldering
• Halle = hall, indoor venue, sports hall

So Boulderhalle means bouldering gym or indoor bouldering hall.

Like many German nouns, it combines smaller words into one longer word.

In a normal German main clause, the finite verb usually comes in second position.

So in:

• Die Boulderhalle öffnet um zehn.

the parts are:

1. Die Boulderhalle = subject
2. öffnet = conjugated verb
3. um zehn = time expression

This is standard German word order.

Öffnet comes from the verb öffnen, which means to open.

Here it is the third-person singular present tense form, used with die Boulderhalle:

• ich öffne
• du öffnest
• er/sie/es öffnet

Since die Boulderhalle is grammatically she/it, you use öffnet.

Because German does not need a separate subject pronoun when the noun itself is already there.

In English, you might say:

• The gym opens at ten.

You do not also say:

• The gym it opens at ten.

German works the same way:

• Die Boulderhalle öffnet um zehn.

The noun Die Boulderhalle is already the subject, so no extra sie/es is needed.

Um is the usual preposition for a specific clock time.

So:

• um zehn = at ten
• um neun Uhr = at nine o’clock
• um halb acht = at half past seven

In this sentence, um zehn means at ten.

Both are possible.

• um zehn
• um zehn Uhr

Both mean at ten o’clock.

German often leaves out Uhr when the meaning is clear, especially in everyday speech. Adding Uhr can sound a little more explicit, but neither version is strange.

Here, öffnet means opens: it describes the action or opening time.

So:

• Die Boulderhalle öffnet um zehn. = The bouldering gym opens at ten.

If you wanted to say is open, German would usually use a different structure, for example:

• Die Boulderhalle ist ab zehn geöffnet. = The bouldering gym is open from ten onward.

So öffnet focuses on the opening event/time, not just the state of being open.

Because zehn is a number word, not a noun.

In German:

• Nouns are capitalized
• most other words are not

So:

• Die → capitalized because it begins the sentence
• Boulderhalle → capitalized because it is a noun
• öffnet → not capitalized
• um → not capitalized
• zehn → not capitalized

A helpful rough guide is:

• öffnet ≈ URFF-net or OEFF-net

Important points:

• ö does not sound like normal English o
• the ffn cluster can feel a little awkward at first
• the -et ending is lightly pronounced

A more exact IPA pronunciation is:

• [ˈœfnət]

And the whole sentence is approximately:

• Dee BOWL-der-hall-uh URFF-net oom tsehn

That is only an approximation, but it can help as a starting point.

Yes. That is also correct.

German often moves time expressions to the front for emphasis:

• Die Boulderhalle öffnet um zehn.
• Um zehn öffnet die Boulderhalle.

Both mean the same thing. But when Um zehn comes first, the verb still stays in second position, so öffnet must come before die Boulderhalle.