Der Einstieg liegt neben der Traverse.

Because Traverse is a feminine noun, but here it is in the dative case.

• dictionary form / nominative: die Traverse
• dative singular: der Traverse

The preposition neben can take either the accusative or the dative. In this sentence it describes a location rather than movement, so German uses the dative:

• neben der Traverse = next to the traverse

So der here does not mean the noun is masculine. It is simply the dative feminine article.

Neben is one of the German two-way prepositions. These prepositions use:

• dative for a static location
• accusative for movement toward a place

In this sentence, the entry point is located next to the traverse; nothing is moving. So German uses the dative:

• Der Einstieg liegt neben der Traverse. = The entry point is next to the traverse.

Compare:

• Der Einstieg liegt neben der Traverse. → location
• Wir stellen den Einstieg neben die Traverse. → movement/placement toward that position

Liegt is the 3rd person singular of liegen, which literally means to lie or to be situated.

In German, liegen is often used for things that are positioned somewhere, especially when talking about location. In English, we often just say is or is located.

So:

• liegt here means something like lies / is situated / is located

You could sometimes say ist in English, but German often prefers liegt when emphasizing physical position.

Compare:

• Der Einstieg liegt neben der Traverse. = The entry point is located next to the traverse.
• Der Einstieg ist neben der Traverse. = understandable, but less idiomatic in many contexts

This is a very common German learner question.

• liegen = to lie, to be lying, to be located
  → no direct object, describes a state/position
• legen = to lay, to put
  → takes a direct object, describes an action of placing something

Examples:

• Das Buch liegt auf dem Tisch. = The book is lying on the table.
• Ich lege das Buch auf den Tisch. = I put the book on the table.

In your sentence:

• Der Einstieg liegt ... = The entry point is located ...

Because Der Einstieg is in the nominative case and matches the verb liegt.

The basic sentence structure is:

• Der Einstieg = subject
• liegt = verb
• neben der Traverse = prepositional phrase telling you where

So the sentence literally works like:

• The entry point
  • is located
    • next to the traverse

The subject is marked by the article der, which here is nominative masculine singular.

Because grammatical gender in German is part of the noun itself, and Einstieg happens to be masculine:

• der Einstieg

This is something you usually have to learn together with the noun. The gender does not always match natural gender or any obvious logic.

So it is best to memorize nouns with their article:

• der Einstieg
• die Traverse

Because in German, all nouns are capitalized.

So:

• der Einstieg
• die Traverse

This is a standard spelling rule in German and one of the first things English speakers notice, since English only capitalizes nouns in special cases.

This sentence follows normal German main-clause word order:

• Der Einstieg = first position
• liegt = second position
• neben der Traverse = the rest

A key rule in German main clauses is that the finite verb must be in second position.

So:

• Der Einstieg liegt neben der Traverse.

You could also move the location phrase to the front, but then the verb still stays second:

• Neben der Traverse liegt der Einstieg.

That version puts more emphasis on the location.

Yes. German is flexible with word order, as long as the finite verb stays in second position in a main clause.

Both are correct:

• Der Einstieg liegt neben der Traverse.
• Neben der Traverse liegt der Einstieg.

The difference is mainly focus:

• Der Einstieg liegt neben der Traverse. → neutral
• Neben der Traverse liegt der Einstieg. → emphasizes the location

Yes. Einstieg can have several related meanings depending on context, such as:

• entry
• entrance point
• start
• boarding point
• access point

In climbing, hiking, transport, or technical contexts, the most natural English translation can vary. So even if the core meaning is clear, the best English wording depends on the situation. That is very normal in German vocabulary.