Learn Hardcore German: Nach der Arbeit treffen wir uns oft in einer kleinen Bar in der Innenstadt. - After work we often meet in a small bar in the city center.

Nach Arbeit (without an article) is unusual here. You normally use nach der Arbeit when you mean “after (my/our/the) work is finished today.”
Nach Arbeit could appear only in very abstract phrases like nach Arbeit suchen (“to look for work”), where Arbeit means work in general, not “today’s working hours.”

Could I say Nach dem Arbeiten instead of Nach der Arbeit? What’s the difference?

You could say nach dem Arbeiten, but it sounds more abstract or process-focused (“after doing work / after the activity of working”).

Nach der Arbeit = after the workday / after your shift / after you finish work (very idiomatic, what people say in everyday speech).
Nach dem Arbeiten = after the act of working (more about the activity itself; less common in this context).

For the everyday “after work, we meet…”, Nach der Arbeit is the natural choice.

Why is the word order Nach der Arbeit treffen wir uns … and not Nach der Arbeit wir treffen uns …?

German main clauses follow the verb-second rule: the finite verb (here: treffen) must be in the second position.

In this sentence:

Nach der Arbeit = first position (a time expression moved to the front for emphasis)
treffen = second position (the conjugated verb)
wir and the rest of the sentence follow afterward.

So:

Correct: Nach der Arbeit treffen wir uns …
Also correct (different emphasis): Wir treffen uns nach der Arbeit …
Incorrect: Nach der Arbeit wir treffen uns … (verb is not in second position).

What does uns do in treffen wir uns? Why isn’t it just treffen wir?

Uns is a reflexive pronoun here. The verb is sich treffen (“to meet each other”), not just treffen.

sich treffen (reflexive) = to arrange to meet / to meet each other
- Wir treffen uns. = We meet (each other).
jemanden treffen (non‑reflexive) = to meet/encounter someone (sometimes by chance), or literally to hit
- Ich treffe ihn. = I meet him / I hit him (depending on context).

So treffen wir uns literally means “we meet ourselves,” but in practice it means “we meet (each other).”
Without uns, treffen wir would be incomplete: you would be missing the object (“we meet who?”).

Could I move oft somewhere else, like Wir treffen uns oft nach der Arbeit or Wir treffen uns nach der Arbeit oft?

Yes, several positions are possible, and they are all grammatically correct. The choice slightly changes the emphasis, not the basic meaning:

Nach der Arbeit treffen wir uns oft in einer kleinen Bar …
Focus on the time first; then you learn that this often happens.
Wir treffen uns oft nach der Arbeit in einer kleinen Bar …
Neutral, common word order. The adverb oft is close to the verb phrase.
Wir treffen uns nach der Arbeit oft in einer kleinen Bar …
Slightly more emphasis on “after work” as the time span in which it often happens.

German adverbs like oft are fairly flexible, but they usually appear after the conjugated verb and before long prepositional phrases unless you move things for emphasis.

Why is it in einer kleinen Bar and not in eine kleine Bar or in einer kleine Bar?

Two things are happening:

Case after “in”
- With location (“where?”), in takes the dative case:
  → in einer kleinen Bar = in a small bar (location)
- With direction (“where to?”), in takes the accusative:
  → in eine kleine Bar gehen = to go into a small bar (movement).
Here it’s a location (where we meet), so you need the dative.
Adjective ending with a feminine dative indefinite article
Feminine singular, dative, with einer:
- Article: einer
- Adjective: kleinen
- Noun: Bar
So the correct form is in einer kleinen Bar.
In eine kleine Bar would be accusative (direction: “(into) a small bar”).
In einer kleine Bar is wrong; the adjective ending must be -en here.

Why is it in der Innenstadt and not in die Innenstadt?

Again, this is about location vs. direction with in:

in der Innenstadt (dative) answers “Where?”
→ “in the inner city / downtown” (location, no movement).
in die Innenstadt (accusative) answers “Where to?”
→ “into the inner city / downtown” (movement towards it).

In the sentence, the bar is located in the inner city, so German uses the dative: in der Innenstadt.

What exactly does Innenstadt mean, and are there synonyms?

Innenstadt is a compound noun:

innen = inside / inner
die Stadt = the city

So die Innenstadt literally means “the inner city,” roughly “city center / downtown.”

Common synonyms / alternatives:

das Stadtzentrum = the city center (a bit more neutral/formal)
die City (colloquial, borrowed from English)
In some regions: die Altstadt = the old town (often overlapping with the center but not always identical).

In this sentence, in der Innenstadt means “in the central area of town / downtown.”

Why are Arbeit, Bar, and Innenstadt capitalized?

In German, all nouns are capitalized, regardless of their position in the sentence.

Arbeit – a noun (work)
Bar – a noun (bar)
Innenstadt – a noun (inner city / downtown)

Pronouns like wir and verbs like treffen are not capitalized (unless they start a sentence). That’s why you see capitals only on the nouns here.

Could I use other words instead of Bar, like Kneipe or Café? Would the sentence still work?

Yes, you can replace Bar with other location nouns, and the grammar (article + adjective ending + case) stays the same:

in einer kleinen Kneipe – in a small pub (more “pub / local bar” feel)
in einem kleinen Café – in a small café (here the noun is neuter, so the article/adjective change: einem kleinen Café)
in einem kleinen Restaurant – in a small restaurant

Only the gender of the noun and therefore the article/adjective forms change, but the structure in + dative stays.