Learn Hardcore Finnish: Minä tunnen tämän kaupungin hyvin.

tuntea = to know/be familiar with people, places, works of art, etc. (acquaintance-type knowing)
tietää = to know a fact (often followed by a clause with että, missä, miten, etc.)

So you say Tunnen tämän kaupungin (I’m familiar with this city), but Tiedän, missä kaupunki on (I know where the city is). Don’t use tiedän with a bare place-name object to mean familiarity.

Do I need to say Minä, or can I drop it?

You can drop it. Finnish usually omits subject pronouns because the verb ending shows the person.

Neutral: Tunnen tämän kaupungin hyvin.
With emphasis/contrast on the subject: Minä tunnen tämän kaupungin hyvin (I, as opposed to someone else, know it well).

Why is it tämän kaupungin and not tämä kaupunki?

Because it’s a direct object in a complete/total sense. Finnish marks a total object most often with the genitive -n. The determiner must agree in case with the noun, so both take -n:

tämä → tämän
kaupunki → kaupungin

Together they form the total object phrase tämän kaupungin.

Could it ever be tätä kaupunkia instead?

Yes, in situations that require the partitive object:

Under negation: En tunne tätä kaupunkia (hyvin).
To emphasize partial/incomplete familiarity: Tunnen tätä kaupunkia jonkin verran.

Partitive (tätä kaupunkia) signals “not the whole” or ongoing/partialness; the genitive/accusative (tämän kaupungin) signals a whole/complete object.

Why does kaupunki become kaupungin?

This is consonant gradation and assimilation:

The genitive singular adds -n.
The cluster nk changes to ng before that -n: kaupunki → kaupungin. This same stem appears in other forms too (e.g., kaupungissa “in the city”).

What exactly is hyvin? Should I use hyvästi?

Hyvin is the regular adverb “well.”
Hyvästi is mostly used as an old-fashioned or set-phrase form meaning “farewell” (Hyvästi! = Goodbye!). Don’t use hyvästi to mean “well” in modern standard Finnish; stick with hyvin.

Can I change the word order? Where can hyvin go?

Word order is flexible for emphasis, but some placements are unnatural.

Neutral/default: Tunnen tämän kaupungin hyvin.
Emphasize the subject: Minä tunnen tämän kaupungin hyvin.
Emphasize the object (“this city in particular”): Tämän kaupungin minä tunnen hyvin.
Emphasize how well: Tunnen hyvin tämän kaupungin.

Don’t split the determiner and noun with an adverb: avoid tämän hyvin kaupungin.

Does tunnen also mean “I feel”?

Yes. Tuntea can mean “to feel/sense.” Examples: Tunnen kipua (I feel pain), Tunnen itseni väsyneeksi (I feel tired). With a place as the object (e.g., a city), it means “to be familiar with/know.” Context decides the meaning.

Is there another natural way to express the same idea?

Yes: Tämä kaupunki on minulle tuttu.
Here tuttu = “familiar,” and minulle = “to me.” This literally says “This city is familiar to me,” which is very natural in Finnish.

What would this sound like in casual spoken Finnish?

Colloquially: Mä tunnen tän kaupungin tosi hyvin.
Key colloquial features: mä (minä), tän (tämän), and intensifier tosi (“very/really”).

What case is tämän—genitive or accusative?

In Finnish, many objects show “total object” with the genitive form. For demonstratives like tämä, the accusative form looks the same as the genitive (tämän). So you can think of tämän here as the accusative (total object), which is syncretic with the genitive in form. For personal pronouns, the accusative is distinct (minut, sinut, hänet, etc.).

How do I say this without “this” (i.e., “I know the city well”)?

Tunnen kaupungin hyvin.
Finnish has no articles, so kaupungin can mean “the city” if context makes it specific. Without context, it can sound a bit vague, so adding tämän is how you make it explicitly “this city.”

How can I emphasize “this city in particular”?

Front the object: Tämän kaupungin minä tunnen hyvin.
This puts strong focus on “this city (as opposed to other cities).”