aki hodo sanposiyasui kisetu ha nai to omoimasu.

ほど marks the standard of comparison. In this pattern, AほどBはない means there is nothing/no B as ... as A.

So:

• 秋ほど散歩しやすい季節はない
• literally: There is no season as easy for walking as autumn
• natural meaning: No season is as good/easy for taking walks as autumn

A very common way to understand it is:

• Aほど〜ない = nothing is as ~ as A

So 秋ほど means as autumn or to the extent of autumn in this comparison.

Because 秋 is directly followed by ほど, which itself marks the comparison target.

So the structure is:

• 秋ほど = as much/as ... as autumn

You do not normally say 秋はほど or 秋がほど here.

Compare:

• 秋ほど涼しい季節はない = There is no season as cool as autumn
• 彼ほど速く走れる人はいない = There is no person who can run as fast as him

In this pattern, the noun before ほど stands on its own.

This is a very useful grammar pattern.

AほどBはない means:

• There is no B as ... as A
• Nothing/no one is more ... than A, depending on translation

In your sentence:

• 秋ほど = as autumn
• 散歩しやすい季節 = a season that is easy to take walks in
• はない = does not exist / there is no

So the full structure is:

• 秋ほど + 散歩しやすい季節 + はない

Literally:

• As for a season easy for walking to the degree of autumn, there is none

Natural English:

• There is no season as pleasant/easy for walking as autumn

This pattern is often used to say something is the best, even though it is phrased negatively.

散歩しやすい means easy to take a walk, easy to go walking, or good for walks.

It comes from:

• 散歩する = to take a walk
• verb stem し
• やすい = easy to do

So:

• 散歩する → 散歩しやすい
• easy to take walks

This does not mean that the walk itself is easy in a literal effort sense only. It often means the conditions are favorable: weather, temperature, comfort, scenery, and so on.

Because やすい attaches to the verb stem, not the dictionary form.

Examples:

• 食べる → 食べやすい
• 行く → 行きやすい
• する → しやすい

Since 散歩する is a suru-verb:

• 散歩する → 散歩しやすい

So 散歩するやすい is ungrammatical.

Here, 季節はない is part of the pattern Aほど〜季節はない.

The は marks 季節 as the topic of the negative statement:

• As for a season ... there is none

It also gives a slight contrastive nuance, which is very common in negative sentences.

So:

• 散歩しやすい季節はない
• There is no season that is easy for walking

Then 秋ほど specifies the comparison:

• There is no season as easy for walking as autumn

Because ない can work as the negative form of ある (to exist / to have).

Here, the sentence is not negating an action. It is saying that such a season does not exist.

So:

• 季節はない = there is no season
• more literally: as for a season, it does not exist

That is why the whole sentence means:

• There is no season as easy for walking as autumn

と 思います means I think.

It softens the statement and makes it sound like the speaker’s opinion rather than an absolute fact.

So compare:

• 秋ほど散歩しやすい季節はない。

  • There is no season as easy for walking as autumn.
  • stronger, more direct

• 秋ほど散歩しやすい季節はないと思います。

  • I think there is no season as easy for walking as autumn.
  • softer, more natural in conversation

Japanese often uses と思います to avoid sounding too blunt.

Yes, that is the natural idea.

Literally, it says:

• There is no season as easy for walking as autumn

But in natural English, this often becomes:

• Autumn is the best season for walking
• I think autumn is the best season for taking walks

So this is a common Japanese way to express a superlative without using a direct word like best.

Yes. A simpler version would be:

• 秋が一番散歩しやすい季節だと思います。
• I think autumn is the easiest season for taking walks.

That said, your original sentence has a slightly more formal or elegant feel:

• 秋ほど散歩しやすい季節はないと思います。

Both are natural, but they feel a little different:

• 一番 = more straightforward
• 〜ほど〜はない = a classic comparison pattern, slightly more emphatic or refined

Yes. 散歩しやすい季節 is a noun phrase meaning:

• a season that is easy for walking
• a walk-friendly season

Japanese often puts modifiers directly before nouns.

So:

• 散歩しやすい = easy to take walks in
• 季節 = season

Together:

• 散歩しやすい季節 = a season that is easy to take walks in

This is the same kind of structure as:

• 住みやすい町 = a town that is easy to live in
• 読みやすい本 = a book that is easy to read

No. Normal Japanese writing would usually be:

• 秋ほど散歩しやすい季節はないと思います。

The spaces in learning materials are often added just to make the parts easier to see.

A natural breakdown is:

• 秋ほど
• 散歩しやすい
• 季節はない
• と思います

But in real Japanese, it would normally appear without spaces.