onsengai wo aruku.

It is read:

おんせんがい を あるく

• 温泉街（おんせんがい） = hot spring town / hot spring resort district
• を = object/path particle
• 歩く（あるく） = to walk

A small pronunciation note: the particle を is pronounced お in modern Japanese, even though it is written を.

温泉街（おんせんがい） does not just mean a single hot spring.

It usually refers to:

• an area built around hot springs
• a resort town with inns, baths, souvenir shops, restaurants, and streets for visitors

So 温泉街を歩く gives the image of walking around the streets of a hot spring resort area.

That is a very common question.

In many sentences, を does mark the direct object, but with some movement verbs it can also mark the place that someone moves through.

So in 温泉街を歩く, を marks the area being traversed:

• 道を歩く = walk along the road
• 公園を走る = run through the park
• 橋を渡る = cross the bridge

So here, 温泉街を歩く means something like:

• walk through the hot spring town
• stroll around the hot spring district

It is not that the speaker is somehow walking the town as a direct object in the English sense. It is a Japanese grammar pattern showing movement through a place.

Because で and を highlight different things.

• 温泉街で歩く would sound unnatural in most cases.
• で marks the place where an action happens.
• を here marks the path or area that is passed through.

Compare:

• 公園で遊ぶ = play in the park
• 公園を歩く = walk through the park

With 歩く, when you want to say the place you move through, を is very natural.

Yes. 歩く is the plain/dictionary form, while 歩きます is the polite form.

• 温泉街を歩く。 = plain style
• 温泉街を歩きます。 = polite style

The plain form may be used in:

• dictionary entries
• casual speech
• written narration
• titles, captions, or notes

So seeing 歩く by itself is completely normal.

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

So 温泉街を歩く。 could mean:

• I walk through the hot spring town.
• We walk through the hot spring town.
• Someone walks through the hot spring town.

Japanese does this very often. If the context already makes the subject clear, it is usually omitted.

Literally, 歩く means to walk. But in context, it can feel more natural in English as:

• walk through
• walk around
• stroll through

Because 温泉街 suggests a sightseeing area, the nuance is often leisurely rather than purely physical movement. So depending on context, stroll through the hot spring town may sound very natural in English.

Yes, though the difference is small.

• 温泉街を歩く = walk through the hot spring town
• 温泉街の中を歩く = walk through/inside the hot spring town

の中 makes the idea of inside that area more explicit.
Without の中, the sentence is simpler and very natural.

So:

• 温泉街を歩く is the more straightforward expression.
• 温泉街の中を歩く adds a little emphasis to being within that area.

Yes, very often. This is a useful pattern.

Examples:

• 道を歩く = walk along the road
• 町を歩く = walk through town
• 浜辺を歩く = walk along the beach
• 森を歩く = walk through the forest

So place + を + 歩く is a common and important structure.

Those spaces are usually just for learners.

Normal Japanese writing would be:

温泉街を歩く。

Japanese is normally written without spaces between words. In textbooks or beginner materials, spaces are sometimes added to make sentence structure easier to see.

By itself, it is still a complete sentence in Japanese, especially in:

• notes
• captions
• diary-style writing
• short descriptions
• narrative style

It can also sound like a simple statement of action, similar to:

• Walk through the hot spring town.
• Walking through the hot spring town.
• I walk through the hot spring town.

Exactly how it is interpreted depends on context, but grammatically it is fine as a standalone sentence.