Ved stadion ligger der en lille bane, hvor min søster plejer at træne om lørdagen.

Because Danish main clauses normally follow the V2 rule: the finite verb must come in second position.

So when the place phrase Ved stadion is moved to the front, the verb has to come right after it:

• Ved stadion ligger der en lille bane ...

If you started with the subject-like element instead, you could also say:

• Der ligger en lille bane ved stadion ...

Both are correct, but they structure the information differently. Fronting Ved stadion puts extra focus on the location.

Here der is a dummy subject, like there in English there is / there are.

Danish often uses this pattern when introducing the existence of something:

• Der er en bog på bordet
• Der ligger en lille bane ved stadion

So der does not mean there in a literal location sense here. It is just part of an existential construction: it introduces something that exists somewhere.

Danish often prefers position verbs when saying where something is:

• ligger = lies / is situated
• står = stands
• sidder = sits / is attached
• er = is

A bane is thought of as a flat area or place, so ligger sounds natural.

So Danish often says something like:

• Skolen ligger i byen
• Der ligger en park her
• Banen ligger ved stadion

Using er would be more neutral, but often less idiomatic in sentences about location.

Ved usually means by, near, or next to.

So Ved stadion means the place is located by / near the stadium, not inside it and not on top of it.

Compare:

• ved stadion = near the stadium
• på stadion = at the stadium / in the stadium area
• i stadionet = inside the stadium

So ved is chosen because the sentence is locating the small field near the stadium.

Because bane is an en-word in Danish, so it takes en in the singular indefinite form:

• en bane
• en lille bane

The adjective lille matches naturally here. It is a very common adjective and behaves a bit irregularly compared with adjectives like stor or længere.

Useful comparison:

• en lille bane
• et lille hus
• den lille bane
• små baner

So the important thing for a learner is: bane is common gender, therefore en bane.

Because hvor introduces a clause referring back to a place.

Here bane is a place where someone trains, so Danish naturally uses:

• en lille bane, hvor min søster plejer at træne

That is similar to English a small field where my sister usually trains.

You could also build the idea differently, for example with som plus a preposition, but hvor is the most natural choice when the noun is a place.

Because after hvor you have a subordinate clause, and subordinate clauses normally do not use main-clause inversion.

So the normal order is:

• hvor min søster plejer at træne

That is:

• hvor = clause introducer
• min søster = subject
• plejer = finite verb
• at træne = infinitive

Compare:

• Main clause: Min søster plejer at træne der
• Question/main-clause inversion: Plejer min søster at træne der?
• Subordinate clause: ..., hvor min søster plejer at træne

Plejer at + infinitive expresses habit or something someone usually does.

So min søster plejer at træne means that this is her usual routine.

It is a very common Danish pattern:

• Jeg plejer at cykle på arbejde
• Vi plejer at spise sent
• Hun plejer at træne om lørdagen

In the present tense, it often corresponds to English usually. In past forms, plejede at often corresponds to used to.

Because pleje normally takes at + infinitive.

So you say:

• plejer at træne
• plejer at læse
• plejer at komme tidligt

This is different from true modal verbs like kan, vil, skal, which usually take the bare infinitive:

• kan træne
• vil træne
• skal træne

So plejer is followed by at, not by a bare infinitive.

Because om + definite singular day is a common way to express a habitual time in Danish.

So:

• om lørdagen = on Saturdays / on Saturday(s) in general

This is different from:

• på lørdag = next Saturday / this coming Saturday

That distinction is very useful:

• Hun træner om lørdagen = it is her regular Saturday habit
• Hun træner på lørdag = she will train this coming Saturday

You may also hear på lørdage, which can also mean on Saturdays, but om lørdagen is especially common for repeated routine actions.

Because hvor min søster plejer at træne om lørdagen is a subordinate clause, and standard Danish spelling uses a comma before subordinate clauses.

So the comma marks the start of the extra clause that describes en lille bane.

This is very common in Danish writing:

• Jeg har en ven, som bor i Aarhus
• Det er huset, hvor hun voksede op
• Ved stadion ligger der en lille bane, hvor min søster plejer at træne om lørdagen