wookinguibento wo kikkake ni, sanpokoosu wo kaeta.

をきっかけに means something like using X as a trigger / prompted by X / taking X as an opportunity.

So:

• ウォーキングイベントをきっかけに = prompted by the walking event / using the walking event as the occasion

It does not always mean a strong logical because. It often means X happened, and that became the starting point for a change.

In this sentence, the idea is:

• there was a walking event
• that event became the reason or trigger
• as a result, the speaker changed their walking route

In the pattern X を きっかけに, the を marks the thing that serves as the trigger.

So the pattern is:

• Noun + をきっかけに

Examples:

• 留学をきっかけに、日本語を勉強し始めた。
  I started studying Japanese prompted by studying abroad.
• 引っ越しをきっかけに、生活を見直した。
  I rethought my lifestyle after moving.

This を is part of a fixed expression. It is not the direct object of きっかけ in the English sense; it is just how this grammar pattern is formed.

The に is also part of the set expression をきっかけに.

Here, に gives the sense of as or on the occasion of. So きっかけに means as a trigger or as an occasion.

You can think of the whole chunk Xをきっかけに as one grammar unit rather than trying to translate each particle separately every time.

A related form is:

• Xをきっかけとして = using X as an opportunity/trigger

This is a bit more formal than をきっかけに.

から and ので usually give a more direct reason or cause:

• 雨だから、行かない。
  I’m not going because it’s raining.

But をきっかけに often means X became the turning point that led to a change.

Compare:

• 運動不足なので、散歩コースを変えた。
  I changed my walking route because I wasn’t getting enough exercise.
  → straightforward reason

• ウォーキングイベントをきっかけに、散歩コースを変えた。
  I changed my walking route after / prompted by a walking event.
  → the event acted as the trigger for the change

So きっかけ often carries a nuance of starting point, motivation, or catalyst, not just simple cause.

Both are possible, but 散歩コース is very natural and compact.

In Japanese, noun + noun compounds are common:

• 通勤電車 = commuter train
• 勉強時間 = study time
• 散歩コース = walking route

散歩コース sounds like a set label: a walking route/course.

散歩のコース is also understandable, but it can sound a little more explanatory or literal:

• the route for a walk

In everyday Japanese, 散歩コース is probably the more natural choice here.

散歩コース means the route someone usually takes for a walk.

It does not mean a formal course like a class. In Japanese, コース can mean:

• route
• course
• plan
• set meal depending on context.

Here it means route:

• 散歩コースを変えた = changed my usual walking route

This is the difference between a transitive and an intransitive verb:

• 変える = to change something
• 変わる = something changes

In the sentence:

• 散歩コースを変えた the speaker is actively changing the route, so 変える is used.

Compare:

• 散歩コースを変えた。
  I changed my walking route.
• 散歩コースが変わった。
  My walking route changed.

The first focuses on the speaker’s action.
The second focuses on the route itself undergoing change.

Japanese often leaves out the subject when it is obvious from context.

So:

• ウォーキングイベントをきっかけに、散歩コースを変えた。

very naturally implies something like:

• I changed my walking route prompted by the walking event or
• We changed our walking route... depending on context.

If needed, you could add a subject:

• 私は、ウォーキングイベントをきっかけに、散歩コースを変えた。

But in normal Japanese, that would often be unnecessary.

Because the sentence is talking about a completed action: the route was changed.

• 変えた = changed
• 変える = change / will change

So:

• ウォーキングイベントをきっかけに、散歩コースを変えた。
  I changed my walking route prompted by the walking event.

If you said:

• ウォーキングイベントをきっかけに、散歩コースを変える。 that would mean:
• I will change my walking route prompted by the walking event or
• I change my walking route for that reason depending on context.

No, the comma is not strictly necessary.

You can write:

• ウォーキングイベントをきっかけに、散歩コースを変えた。
• ウォーキングイベントをきっかけに散歩コースを変えた。

Both are fine.

The comma just makes the sentence easier to read by separating the introductory phrase:

• ウォーキングイベントをきっかけに = prompted by the walking event from the main action:
• 散歩コースを変えた = changed my walking route

Yes, to some extent.

The most natural order is:

• ウォーキングイベントをきっかけに、散歩コースを変えた。

But Japanese word order is flexible, especially for phrases before the verb. For example:

• 散歩コースを、ウォーキングイベントをきっかけに変えた。

This is grammatically possible, but it sounds a bit more marked because it puts focus on 散歩コースを first.

In ordinary conversation or writing, the original order is smoother and more natural.

Yes, it is understandable and fairly natural, especially in modern Japanese where many event names use loanwords.

ウォーキングイベント means a walking event, such as:

• a community walking day
• a health-promotion walking event
• an organized walking activity

Depending on context, other expressions might also be used, such as:

• 歩くイベント
• ウォーキング大会
• 散策イベント

But ウォーキングイベント is perfectly reasonable and easy to understand.