asa ni sanposuruno ha kimoti ga ii desu.

散歩する is a suru-verb.

• 散歩 = a walk, a stroll
• する = to do

So 散歩する means to take a walk, to go for a walk, or to stroll.

It is a little different from 歩く, which simply means to walk.
散歩する usually suggests walking for pleasure, relaxation, or light exercise.

Here, の turns the verb phrase into a noun-like phrase.

• 散歩する = to take a walk
• 散歩するの = taking a walk / the act of taking a walk

This is called nominalizing the verb.

So in this sentence, 朝に散歩するの means taking a walk in the morning.

Because the whole phrase 朝に散歩するの is being made the topic of the sentence.

• 朝に散歩するのは = as for taking a walk in the morning...

Then the rest of the sentence comments on that topic:

• 気持ちがいいです = feels good / is pleasant

So the structure is basically:

• [Taking a walk in the morning]
  • is pleasant

Not always.

With time words like 朝, Japanese often omits に, especially in everyday speech.

So these are both understandable:

• 朝に散歩するのは気持ちがいいです
• 朝、散歩するのは気持ちがいいです

In natural conversation, the version without に is often more common.

So 朝に is not wrong here, but learners should know that 朝 by itself is also very natural.

気持ちがいい is a very common expression meaning:

• feels good
• is pleasant
• is refreshing

In this sentence, it means that taking a walk in the morning gives a pleasant feeling.

The word 気持ち literally means feeling or sensation, but the whole phrase 気持ちがいい should usually be learned as a set expression.

Because 気持ちがいい is the normal expression.

Here, が marks 気持ち as the grammatical subject inside that expression.

• 気持ちがいい = it feels good

If you say 気持ちはいい, it sounds more contrastive, like:

• The feeling is good, but...

So for a simple neutral statement, 気持ちがいい is the standard form.

Yes. いい is an い-adjective, and in polite speech you can add です after it.

• plain: いい
• polite: いいです

So:

• 気持ちがいい = plain
• 気持ちがいいです = polite

Also, いい is the common spoken form of よい.
So 気持ちがよいです is also possible, but 気持ちがいいです is more common in everyday Japanese.

Usually it sounds like a general statement.

So it means something like:

• Taking a walk in the morning feels good
• Walking in the morning is pleasant

It does not usually mean one particular morning unless the context makes that clear.

If you wanted to talk about a specific morning, you would normally use something like:

• 今朝の散歩は気持ちがよかったです
  = This morning's walk felt good

Yes.

• 散歩するのは気持ちがいいです
• 散歩することは気持ちがいいです

Both are grammatically correct.

The difference is mostly nuance:

• の often sounds a bit more natural and conversational
• こと can sound a bit more formal, abstract, or explanatory

In this sentence, の is very natural.

Yes, you can, and it is very natural.

Compare:

• 朝に散歩するのは気持ちがいいです
• 朝に散歩するのが気持ちいいです

The difference is small:

• のは presents taking a walk in the morning as the topic, then comments on it
• のが treats it more directly as the thing that feels good

In English, both are very close:

• As for taking a walk in the morning, it feels good
• Taking a walk in the morning feels good

In everyday Japanese, many people may prefer the のが気持ちいい version because it sounds a little more direct and natural.