Mañana quiero pasear por otra ciudad con mi amigo.

Spanish often puts time expressions near the beginning to set the scene first. So Mañana quiero pasear por otra ciudad con mi amigo is very natural.

You could also say:

• Quiero pasear por otra ciudad con mi amigo mañana.

That is also correct. Putting mañana first just gives it a little more emphasis.

No. Mañana can mean either:

• tomorrow
• morning

Context tells you which one is meant.

For example:

• Mañana quiero pasear... = Tomorrow I want to go for a walk...
• Por la mañana quiero pasear... = In the morning I want to go for a walk...

Very often, la mañana refers to the morning, while mañana by itself often means tomorrow.

After querer when you want to say to want to do something, Spanish uses an infinitive.

So the pattern is:

• querer + infinitive

Examples:

• quiero pasear = I want to walk / go for a stroll
• quiero comer = I want to eat
• quiero viajar = I want to travel

Paseo is not the infinitive. It can be a noun (a walk / stroll) or a verb form (I walk / I stroll) depending on context, but after quiero, you need pasear.

Pasear usually means to go for a walk, to stroll, or to walk around for pleasure.

It is different from some other walking verbs:

• caminar = to walk
• andar = to walk / go around
• pasear = to stroll, walk around, go out walking for enjoyment

So quiero pasear sounds more like walking around in a relaxed way, not just walking to get somewhere.

Here, por shows movement through, around, or in different parts of a place.

So pasear por otra ciudad means something like:

• stroll around another city
• walk through another city

This is very common with movement inside a place:

• caminar por el parque = walk through the park
• pasear por Madrid = stroll around Madrid

Because the idea is not simply going to a city or being in a city. The sentence focuses on moving around inside it.

Compare:

• ir a otra ciudad = to go to another city
• estar en otra ciudad = to be in another city
• pasear por otra ciudad = to stroll around another city

So por is the best choice when the action is movement through or around a place.

In Spanish, otro / otra usually replaces the article.

So you say:

• otra ciudad
• otro libro
• otra idea

Not:

• una otra ciudad

This is a common difference from English. Even though English says another city, Spanish just uses otra ciudad without una.

Because ciudad is a feminine noun.

So the adjective or determiner must agree with it:

• otra ciudad
• esta ciudad
• una ciudad bonita

Even though ciudad does not end in -a, it is still feminine. Gender in Spanish does not always depend only on the ending.

Before a singular noun, Spanish usually uses possessives like mi, tu, su directly, without an article.

So:

• mi amigo = my friend
• mi casa = my house
• tu libro = your book

You do not normally say el mi amigo or un mi amigo in standard modern Spanish.

Yes. Amigo is masculine, so it refers to a male friend.

If the friend were female, it would be:

• mi amiga

Because mi does not change, the noun shows the gender:

• mi amigo = my male friend
• mi amiga = my female friend

The word order is fairly flexible.

You could also say:

• Mañana quiero pasear con mi amigo por otra ciudad.

That is also correct.

Both versions are natural. The difference is mostly about rhythm or what you want to highlight slightly:

• por otra ciudad earlier = a bit more focus on the place
• con mi amigo earlier = a bit more focus on the companion

No, because mi amigo here comes after con, not as a direct object.

The personal a is used mainly with direct objects referring to people:

• Veo a mi amigo. = I see my friend.

But in your sentence:

• con mi amigo = with my friend

So no personal a is needed.

Quiero is perfectly normal here. It simply means I want to.

But if you want to sound softer, more tentative, or more polite, Spanish often uses:

• me gustaría = I would like

For example:

• Mañana me gustaría pasear por otra ciudad con mi amigo.

That sounds a bit less direct than quiero, but both are correct.

It suggests that the plan involves being in another city and walking around there, but the sentence itself does not focus on the travel part.

If you want to make the idea of going there explicit, you could say something like:

• Mañana quiero ir a otra ciudad y pasear por ella con mi amigo.

Your original sentence is more about the activity of strolling around once there.