i deungsanroreul jeoldae tteonaji ma.

이 means this and directly modifies the noun that follows it.

• 이 등산로 = this hiking trail
• Compare:
  • 이 = this
  • 그 = that
  • 저 = that over there

So 이 등산로를 means this trail as the thing being referred to in the sentence.

등산로 means mountain trail, hiking trail, or path for hiking.

It is made up of:

• 등산 = mountain climbing / hiking
• 로 = route / road / path

So 등산로 is a trail people follow while hiking.

In this sentence, 를 marks 등산로 as the object of 떠나다.

Korean often uses 을/를 with 떠나다 to mean leave a place:

• 집을 떠나다 = leave home
• 고향을 떠나다 = leave one’s hometown
• 자리를 떠나다 = leave one’s seat
• 등산로를 떠나다 = leave the trail

Even though in English we often think of a place as something you go away from, Korean commonly marks it with 을/를 after 떠나다.

절대 means something like absolutely, never, or under no circumstances.

In commands, it strongly emphasizes the prohibition:

• 절대 떠나지 마 = Absolutely do not leave
• 절대 잊지 마 = Never forget
• 절대 하지 마 = Never do it

A very important point: 절대 is normally used with a negative expression. So it sounds natural with 떠나지 마, not with a positive verb.

떠나지 마 is the informal negative imperative form, meaning don’t leave.

Breakdown:

• 떠나다 = to leave
• stem: 떠나-
• -지 마 = don’t do...

So:

• 떠나다 → 떠나지 마 = don’t leave

This pattern is extremely common:

• 가지 마 = don’t go
• 먹지 마 = don’t eat
• 만지지 마 = don’t touch

So the whole sentence is built as:

• 이 등산로를 = this trail
• 절대 = absolutely / never
• 떠나지 마 = don’t leave

The short answer is that -지 마 is the standard spoken pattern for don’t do...

Historically, it comes from 말다, but learners should usually treat -지 마 as a fixed grammar pattern.

So:

• 떠나지 마 = correct and natural
• You do not normally need to think of it as separately conjugating 말다 in everyday use

For practical learning, just memorize:

• verb stem + -지 마

Yes. 떠나지 마 is informal, so it would be used:

• to a friend
• to someone younger
• in dramatic speech
• in urgent situations
• in warnings where bluntness is natural

A more polite version would be:

• 이 등산로를 절대 떠나지 마세요.

That would be better for:

• strangers
• customers
• public announcements
• speaking politely in general

Yes, 절대 is somewhat flexible in position, though some placements sound more natural than others.

These are natural:

• 이 등산로를 절대 떠나지 마.
• 절대 이 등산로를 떠나지 마.

Both mean essentially the same thing: Never leave this trail.

Putting 절대 right before the negative verb is very common because it emphasizes the prohibition clearly.

It works, and the meaning is clear: do not leave this hiking trail.

However, in Korean, if you mean don’t go off the trail, a very common and natural verb is 벗어나다:

• 이 등산로를 절대 벗어나지 마.

That can sound more specifically like:

• don’t stray from the trail
• don’t step off the trail

By contrast, 떠나다 can feel a bit broader, like leave or depart from. So your sentence is understandable and correct, but 벗어나지 마 is often especially natural for trails, paths, rules, or boundaries.

Because Korean often omits the subject when it is obvious from context.

In a command like this, the subject is understood as you. Korean usually does not say you explicitly unless it needs emphasis.

So:

• 이 등산로를 절대 떠나지 마. naturally means
• Don’t ever leave this trail.

The hidden subject is basically you, but Korean does not need to state it.

It sounds like a strong warning, especially in a situation involving safety or danger.

For example:

• a hiking guide warning someone
• a parent warning a child
• a survival situation
• a sign or spoken instruction in an emergency

Because of 절대 and the plain-form command -지 마, it sounds firm and serious:

• Do not leave this trail under any circumstances.

So the tone is not casual in meaning, even though the grammar level is informal.