noseondoreul bogo naseoya uriga bandae banghyang seunggangjange seo isseossdaneun geol arasseo.

-고 나서야 adds a strong nuance of only after doing something or not until doing something.

So 노선도를 보고 나서야 means:

• only after looking at the route map
• it wasn’t until we looked at the route map that...

The -야 part gives that feeling of delayed realization. Without it, 보고 나서 would just mean after looking in a more neutral, time-order sense.

• 보고 나서 알았어 = I found out after looking
• 보고 나서야 알았어 = I only found out after looking / It wasn’t until I looked that I realized

Because 보다 takes a direct object, and 노선도 is the thing being looked at.

So:

• 노선도 = route map / line map
• 노선도를 보다 = to look at the route map

That is why -를 appears here.

노선도 means a route map or line map, especially for things like subways, trains, or buses.

It is made of:

• 노선 = route, line
• 도 = map, diagram

In this sentence, it most likely means something like a subway line map.

Korean often stacks nouns together to make a noun phrase.

So:

• 반대 = opposite
• 방향 = direction
• 승강장 = platform

Together, 반대 방향 승강장 means the platform for the opposite direction.

You can think of it as a compact noun phrase:

• opposite-direction platform

This kind of noun stacking is very common in Korean.

Literally, yes, it is was standing on the platform, but in context it often means we were there on the platform, probably waiting there.

Breakdown:

• 승강장에 = at/on the platform
• 서 있었다 = was standing

In Korean, 서 있다 is commonly used for the state of being upright in a place. In everyday context, it can sound very natural even where English might say:

• we were on the platform
• we were standing on the platform
• we were waiting on the platform

So the literal form is were standing, but the natural meaning may be broader.

Here, 서 있었다는 걸 알았어 means realized that we had been standing...

The pattern is:

• clause + 다는 것 = the fact that...
• 것을 often becomes 걸 in casual speech
• clause + 다는 걸 알다 = to know/realize that...

So:

• 우리가 반대 방향 승강장에 서 있었다는 걸 알았어 = I realized that we were standing on the opposite-direction platform

Using -다고 알았어 would not work the same way here. 알다 usually connects naturally with -는지, -다는 것, or a noun-like clause. In this sentence, -다는 걸 is the normal structure.

걸 is a casual spoken contraction of 것을.

So:

• 서 있었다는 것을 알았어 = I realized that...
• 서 있었다는 걸 알았어 = same meaning, but more natural in casual speech

This contraction is extremely common in everyday Korean.

A few similar contractions:

• 것이 → 게
• 것을 → 걸
• 것은 → 건

우리가 uses the subject marker -가, which often sounds more natural when identifying or newly recognizing who was in that situation.

Here the speaker is realizing a fact:

• 우리가 ... 서 있었다 = we were standing...

This has a slightly focused, factual feel: it was us who were standing there.

If you used 우리는, it would sound more like setting we up as the topic, which is possible in some contexts, but 우리가 fits this discovery-style sentence very well.

The subject of 알았어 is not stated, but it is understood from context, usually I.

So the sentence contains two layers:

1. Embedded clause:

   • 우리가 반대 방향 승강장에 서 있었다
   • we were standing on the opposite-direction platform

2. Main clause:

   • 알았어
   • realized / found out

Putting it together:

• I realized that we were standing on the opposite-direction platform.

Korean often leaves out pronouns like I when they are obvious.

Because the realization happened at a particular moment in the past.

• 알다 = to know
• 알았어 = knew / found out / realized

In this kind of sentence, 알았어 is usually best translated as realized or found out, not simply knew.

So the idea is:

• first, we were standing on the wrong platform
• then, after looking at the map, I realized it

알았어 is in the casual informal style, often used with friends, family, or people you speak comfortably with.

More polite versions would be:

• 알았어요
• 알게 되었어요 in some contexts
• 알았습니다 in a more formal situation

So this sentence has a natural, conversational tone.

Yes, that is a very good translation.

That English version captures the important nuance of 보고 나서야, which is the idea of only then or not until then.

A few natural translations are:

• It wasn’t until we looked at the route map that we realized we were standing on the platform for the opposite direction.
• Only after looking at the route map did we realize we were on the wrong-direction platform.
• After checking the route map, we finally realized we were standing on the platform for the opposite direction.

All of these work, though the first two capture the Korean emphasis especially well.