Learn Hardcore Russian: За зоопарком есть маленький парк с аттракционами, качелями и детской горкой. - Behind the zoo there is a small park with rides, swings, and a children’s slide.

за
- accusative = movement to a place (where to?)
  - Я иду за зоопарк. – I am going (to) beyond the zoo.
за
- instrumental = location (where?)
  - За зоопарком есть парк. – There is a park behind the zoo.

In this sentence we are describing a location, not movement, so зоопарком is in the instrumental case.

What is the difference between за зоопарком and something like за зоопарк?

за зоопарком (instrumental) = behind the zoo (static location).
за зоопарк (accusative) would normally mean to beyond the zoo (direction / movement).

So:

Мы живём за зоопарком. – We live behind the zoo. (where?)
Мы поедем за зоопарк. – We will go to the area beyond the zoo. (where to?)

In your sentence, we’re just stating where the park is, so the static за зоопарком is correct.

Why do we need есть here? Could we say За зоопарком маленький парк... without есть?

Both are possible, but there is a nuance:

За зоопарком есть маленький парк...
Neutral, standard existential construction: “There is a small park behind the zoo…”
За зоопарком маленький парк с аттракционами…
This is shorter, more “descriptive” or literary; Russian allows dropping есть when the existence is obvious from context or when you sound a bit more “compressed”.

In everyday speech, есть is very common in “there is/are” sentences, especially when introducing new information. Omitting есть is more typical in:

short signs or notes,
more literary styles,
or when the context is very clear.

Your version with есть is perfectly natural and slightly more neutral.

Why is маленький парк in the nominative case? Isn’t this like an object?

In Russian “there is/are” sentences with есть, the thing that exists is usually the subject in the nominative:

Есть парк. – There is a park.
Есть маленький парк. – There is a small park.

Adding a location in front doesn’t change that:

За зоопарком есть маленький парк.
Behind the zoo (location) + there exists (есть) + a small park (subject in nominative).

So маленький парк is in the nominative because it’s the grammatical subject: the thing that “exists” behind the zoo.

What case are аттракционами, качелями, детской горкой in, and why?

All three are in the instrumental case because they follow с in the sense “with, having, including”:

с аттракционами – with rides
с качелями – with swings
с детской горкой – with a children’s slide

The instrumental case is used after с when it means “together with / equipped with / having”:

чай с лимоном – tea with lemon
дом с садом – a house with a garden
парк с аттракционами – a park with rides

So:

аттракционами – instrumental plural of аттракцион
качелями – instrumental plural of качели
детской горкой – instrumental singular of детская горка, with adjective and noun both in the feminine instrumental.

Why is качелями plural? Is there no singular form for “swing” in Russian?

Качели is one of those Russian nouns that exists only in the plural (pluralia tantum), even if you mean just one set of swings.

Nominative plural: качели
Instrumental plural: качелями

You say:

Во дворе есть качели. – There is a swing set / some swings in the yard.
Парк с качелями. – A park with swings.

There is no natural everyday singular form like качель for one swing; speakers still use the plural and rely on context (or add descriptive words) if they need to be more specific.

What exactly does аттракционы mean here? “Attractions” or specifically amusement rides?

In everyday Russian, аттракционы in the context of a park almost always means amusement rides:

carousels
roller coasters
other mechanical rides for children or adults

While literally it could be “attractions,” in most neutral, real-world contexts like парк с аттракционами, people understand it as rides, not just “interesting things.”

What is the gender of зоопарк, парк, аттракцион, качели, горка, and how does that affect the adjectives маленький and детской?

Genders:

зоопарк – masculine
парк – masculine
аттракцион – masculine
качели – grammatically plural, no singular; treated like feminine plural in adjective agreement (новые качели)
горка – feminine

Adjectives must agree with nouns in gender, number, and case:

маленький парк
- маленький – masculine, singular, nominative
- парк – masculine, singular, nominative
детской горкой
- детской – feminine, singular, instrumental
- горкой – feminine, singular, instrumental

So you see the agreement:

парк → маленький (masc nom)
горкой → детской (fem instr)

Why is it детской горкой, not детская горка?

The base phrase is детская горка – “a children’s slide” (nominative case, used as subject):

Там есть детская горка. – There is a children’s slide.

In your sentence, детской горкой is part of the phrase с детской горкой (“with a children’s slide”), and с requires the instrumental case:

детская горка (nominative) → детской горкой (instrumental)
- детская → детской (feminine adj, nom → instr)
- горка → горкой (feminine noun, nom → instr)

So the change is purely grammatical: same meaning, different case because of the preposition с.

Could we replace есть with находится? For example: За зоопарком находится маленький парк... – is that OK, and what is the difference?

Yes, За зоопарком находится маленький парк... is grammatically correct.

Difference in nuance:

есть – neutral “there is/are”; simply states existence:
- За зоопарком есть маленький парк... – There is a small park behind the zoo.
находится – literally “is located, is situated”; a bit more formal/“informative” about location:
- За зоопарком находится маленький парк... – A small park is located behind the zoo.

In everyday speech, both are fine. есть sounds slightly more colloquial and neutral; находится emphasizes the location a bit more and can feel slightly more formal or “textbook-like.”

Can the word order change, for example: Маленький парк с аттракционами, качелями и детской горкой есть за зоопарком? Does the meaning change?

Yes, the word order can change, because Russian word order is flexible. All of these are possible:

За зоопарком есть маленький парк с аттракционами...
Neutral, common; introduces the park as something that exists behind the zoo.
За зоопарком находится маленький парк с аттракционами...
Similar meaning, a bit more “location-focused” and formal.
Маленький парк с аттракционами... находится за зоопарком.
Emphasizes the park first, then tells you where it is. Could be used if the park is already known from context.
Маленький парк с аттракционами... есть за зоопарком.
Grammatically OK but unusual; есть is rarely used this late in the sentence in such a context. Native speakers would more likely drop есть here:
- Маленький парк с аттракционами... за зоопарком.

So: word order can change, but the given order (За зоопарком есть...) is the most natural for introducing new information.

Why are commas used between аттракционами, качелями и детской горкой?

This is a standard list of three items in Russian:

с аттракционами, качелями и детской горкой

The rules are similar to English:

Put commas between items in a list.
Put и (“and”) before the last item.
No comma before и in normal lists.

So:

с аттракционами, качелями и детской горкой
= with rides, swings, and a children’s slide.

The commas simply separate the elements of the list.