Learn Hardcore Japanese: saisyo ha kintyousite ita noni, kaizyou ni tuitara otituita. - She was nervous at first, but she calmed down after arriving at the venue.

It marks a topic and sets up a contrast: “As for the beginning/at first…”. Using は here contrasts the initial state (nervous) with what happened later (calm). It’s different from 最初に, which is more like “first(ly)” in a sequence of actions. Here you’re not ordering actions; you’re describing a state at a time, so 最初は is natural.

Why is it 緊張していた and not 緊張した?

緊張していた (te-iru past) describes a continuing state in the past: “was nervous (over a period)”.
緊張した is more like “got/became nervous” (a single event) or a simple past without the ongoing nuance. Because the sentence contrasts a prolonged initial state with a later change, 緊張していた fits better.

What nuance does のに add compared with けど/けれど(も)?

のに = “even though/contrary to expectation.” It’s stronger and often carries a sense of surprise or mild frustration at the mismatch between A and B.
けど/けれど(も) = “but/though.” Milder, more neutral link. You could say 最初は緊張していたけど… for a softer contrast. With nouns and na-adjectives you’d use なのに (e.g., 静かなのに), but with verbs and i-adjectives it’s just のに.

Is it okay to say 最初は緊張していたけど、会場に着いたら落ち着いた instead?

Yes. It’s perfectly natural and a bit less emphatic than のに. The meaning remains the same; the tone is just softer.

Why is it 会場に and not 会場へ with 着く?

With 着く (“arrive”), に is the default and most natural particle to mark the destination reached. へ is possible but less common here and focuses on direction rather than the endpoint. For arrivals, prefer X に着く.

Why 着いたら instead of 着いたとき? What’s the difference?

Vたら often marks “when/once (after) X happened, then Y happened” with a sense that X triggers Y, sometimes unexpectedly.
Vたとき is more neutral: “at the time when X happened,” just locating Y in time. Both work here, but 着いたら highlights the arrival as the trigger for calming down. 着いたとき feels slightly more neutral/chronological.

Could I use 着くと here?

Yes: 会場に着くと、落ち着いた is possible. A と B can describe what is discovered or what happens inevitably when A occurs. Nuance:

と suggests a more automatic or immediate result/discovery.
たら emphasizes “upon/once” and is common for one-time past sequences with a bit of “and then” flavor. Both are acceptable; たら is very natural in personal narratives.

What about 着いてから?

Vてから = “after doing X, (then) Y,” emphasizing sequence and that Y occurs only after X is fully completed. 会場に着いてから落ち着いた is fine and sounds slightly more methodical/ordered than 着いたら.

Is there any tense mismatch? Why are there so many past forms?

No mismatch. Japanese often uses past forms in both clauses to narrate a sequence:

緊張していた (past continuous state),
着いたら (past-based conditional),
落ち着いた (past event). Together they describe “I was nervous at first; when I arrived, I calmed down.”

Why is there no subject like “I”?

Japanese frequently omits subjects when clear from context. Here, the subject is understood to be the speaker. You could add 私は at the start, but it’s usually unnecessary unless you need to contrast subjects.

Is 落ち着く transitive or intransitive? Could it mean “calmed someone”?

落ち着く is intransitive: “to become calm / settle down.” 落ち着いた = “(I) calmed down.” To say “calmed someone (else),” use 落ち着かせた (causative), e.g., 子どもを落ち着かせた.

Could I say 落ち着けた instead of 落ち着いた?

You could, but the nuance changes:

落ち着いた = the outcome/state: “I became calm.”
落ち着けた (potential) = “I was able to calm down,” emphasizing ability/opportunity rather than the simple result. The original sentence naturally just reports the result.

How would I make the sentence polite?

Change the final verb (and optionally all verbs) to the polite form:

最初は緊張していたのに、会場に着いたら落ち着きました。 Keeping all verbs consistently polite is stylistically cleaner.

Why are there spaces between the words?

They’re for learner readability. Standard Japanese writing does not use spaces between words; you’d normally see it as: 最初は緊張していたのに、会場に着いたら落ち着いた。

When do I use なのに vs のに?

Use なのに after nouns and na-adjectives; use のに after verbs and i-adjectives.

Noun/na-adj: 学生なのに / 静かなのに
Verb/i-adj: 緊張していたのに / 忙しいのに

Could I use synonyms like ほっとした or 安心した instead of 落ち着いた?

Yes, with nuance differences:

落ち着いた: became calm/composed (general calmness).
ほっとした: felt relieved (release of tension).
安心した: felt reassured (sense of safety/relief). Pick the one that best matches what you want to highlight.