Купель находится рядом с душем.

Because рядом с requires the instrumental case.

• Base form: душ
• Instrumental singular: душем

So:

• рядом с душем = next to / beside the shower

This is a very common pattern:

• рядом с домом = next to the house
• рядом с ванной = next to the bathtub
• рядом с окном = next to the window

A good chunk to memorize is рядом с + instrumental.

Купель is in the nominative case because it is the subject of the sentence — the thing being described as being somewhere.

In Купель находится рядом с душем:

• Купель = the subject
• находится = is located / is situated
• рядом с душем = next to the shower

So the basic structure is:

[subject in nominative] + [location verb] + [place expression]

Yes, it often can be omitted in everyday Russian.

These two are both natural:

• Купель находится рядом с душем.
• Купель рядом с душем.

The version with находится sounds a bit more explicit, formal, or descriptive, like is located or is situated.

The shorter version is very common in speech when simply stating location.

So:

• Купель рядом с душем. = more conversational
• Купель находится рядом с душем. = slightly more formal or precise

Not exactly.

• находится means is located, is situated, or literally finds itself
• есть means there is / there are, or sometimes is, but Russian often does not use есть the way English uses is

For location, Russian usually prefers:

• Книга на столе. = The book is on the table.
• Купель рядом с душем. = The font/tub is next to the shower.

Using находится adds the idea of physical location more explicitly.

So in this sentence, находится is not just a filler verb like English is; it specifically expresses location.

Рядом originally means something like nearby / beside, and in this pattern it works together with с to mean next to or beside.

You can think of рядом с as a fixed expression:

• рядом с магазином = next to the store
• рядом с кроватью = next to the bed
• рядом с душем = next to the shower

So even though it looks like two separate words, learners usually do best treating it as one unit:

рядом с + instrumental

Yes, купель is a feminine noun.

In Russian, many nouns ending in ь can be either masculine or feminine, so you often just have to learn the gender with the word.

Here, купель is feminine. That matters for agreement in other sentences, for example:

• Большая купель = a big font/tub
• Купель была рядом с душем = The font/tub was next to the shower

So the soft sign ь does not automatically tell you the gender by itself.

Because душ is a masculine noun, and one common instrumental singular ending for masculine nouns is -ом or -ем.

Here:

• душ → душем

Why -ем instead of -ом? After certain sounds, Russian often uses -ем. For learners, the most important thing here is simply to learn the full form:

• с душем = with a shower
• рядом с душем = next to the shower

Even if the detailed spelling rules come later, this sentence is a good example of the instrumental after с in a location phrase.

Yes. Russian word order is more flexible than English word order.

These are all possible, depending on emphasis:

• Купель находится рядом с душем.
• Рядом с душем находится купель.

The first version is the most neutral if you are talking about the font/tub and then saying where it is.

The second version puts more focus on the location, almost like:

• Next to the shower is the font/tub.

So the original sentence uses normal, neutral word order.

Находится is pronounced approximately like na-HO-deet-sa.

About -ся:

This ending is the reflexive marker. In many verbs, it gives meanings like:

• oneself
• a state
• a passive-like meaning
• something existing in a place

In находиться, the meaning is to be located / to be situated.

So:

• находить = to find
• находиться = to be located

They are related historically, but as a learner, it is best to memorize находиться as its own verb meaning to be located.

Usually душ means shower in a general sense, depending on context:

• the shower fixture
• the place where the shower is
• the act of taking a shower in some contexts

In this sentence, рядом с душем most naturally means next to the shower area / next to the shower.

Russian often relies on context rather than making the distinction explicit every time.

Yes, but in casual speech many speakers would probably shorten it to:

• Купель рядом с душем.

The longer sentence with находится is still completely natural, especially in:

• descriptions of rooms or buildings
• written information
• tours
• instructions
• more formal speech

So both are correct; the full version just sounds a bit more descriptive or formal.