Wir bouldern den Boulder gemeinsam aus.

Because in German, all nouns are capitalized.

• Boulder is a noun.
• bouldern is a verb.

So this is normal German spelling, not a special climbing rule.
Compare:

• der Boulder = the boulder / the boulder problem
• wir bouldern = we are bouldering

Not necessarily. In climbing German, der Boulder often means a boulder problem or short climbing route, not just a literal rock.

So in this kind of sentence, learners should usually understand Boulder as a piece of climbing jargon. Depending on context, it can mean:

• the actual boulder
• the route/problem on it

In climbing speech, that shorter use is very common.

Because den Boulder is the direct object of the verb, so it is in the accusative case.

Boulder is masculine in German climbing usage:

• nominative: der Boulder
• accusative: den Boulder
• dative: dem Boulder

So:

• Der Boulder ist schwer. = The boulder/problem is hard.
• Wir bouldern den Boulder aus. = We finish/work through the boulder problem.

Here aus is not just the separate word out in the English sense. It is the separable prefix of the verb ausbouldern.

That prefix often adds the idea of:

• doing something to completion
• finishing it fully
• exhausting the possibilities of it

So ausbouldern suggests something like:

• to finish a boulder problem
• to work a boulder all the way through
• to climb it out completely

The exact nuance depends on the speaker and the climbing context, but it usually has a completion feeling.

Because ausbouldern is a separable verb.

In a normal main clause, German does this:

• the conjugated verb part goes in the usual verb position
• the prefix goes to the end

So:

• infinitive: ausbouldern
• main clause: Wir bouldern den Boulder gemeinsam aus.

This works just like:

• aufstehen → Ich stehe früh auf.
• einkaufen → Wir kaufen heute ein.

So the sentence structure is completely normal for a separable verb.

It is understandable, but it is also jargon-heavy and fairly colloquial. It sounds like climbing-specific language.

A learner should recognize that this is not the kind of verb you would expect in general everyday German. It belongs more to:

• sports slang
• climbing community language
• informal speech among people who boulder

So yes, it can be natural in the right context, but it is not a basic textbook verb.

Yes, it does sound repetitive, especially to an English speaker, because both words come from the same source. But in German this kind of repetition can still happen, especially in specialist language.

Here the two words do different jobs:

• bouldern = the activity / verb
• Boulder = the specific problem / noun

So the sentence is structurally fine, even if it sounds a bit playful or jargon-heavy. In more neutral German, people might choose a different verb, for example:

• Wir schaffen den Boulder gemeinsam.
• Wir lösen den Boulder gemeinsam.
• Wir klettern den Boulder gemeinsam.

Those may sound less repetitive, depending on the speaker and context.

Gemeinsam means together.

It is an adverb modifying the action, so it tells you how they are doing it: they are doing it together.

In German, its position is somewhat flexible. For example, these are all possible depending on emphasis:

• Wir bouldern den Boulder gemeinsam aus.
• Wir bouldern gemeinsam den Boulder aus.
• Gemeinsam bouldern wir den Boulder aus.

The original sentence is perfectly fine. Putting gemeinsam before aus is a very natural placement.

It is grammatically fine, but stylistically it sounds very specific to climbing culture.

A native speaker outside that context might find it:

• a bit technical
• a bit playful
• slightly unusual because of bouldern ... Boulder

Inside a climbing context, though, it can sound quite natural.

So the best way to think about it is:

• correct German: yes
• neutral everyday German: not really
• natural climbing jargon: yes, very possibly