V+ 으러/러 가는데

It is used to ask a question or to propose to the listener while mentioning the purpose of the speaker moving to his destination in the preceding clause.

For ‘-으러/러 가는데’, if the stem of an action verb ends with a vowel or ‘ㄹ’, you use ‘-러 가는데’,w with another consonant you use ‘-으러 가는데’.

나 지금 도서관에 책 빌리러 가는데 같이 갈래?듣기
I’m going to the library to borrow a book. Do you want to go with me?

나 이번에 미국에 처음 놀러 가는데 어디에 가면 좋을까?듣기
This is my first trip to America. Where should I go?

오늘 수업 끝나고 과 친구들하고 농구 보러 가는데 너도 시간되면 같이 가자.듣기
I’m going to play basketball with my classmates after class. If you have time, let’s go together.

Conversation:

너 토마토에 소금 뿌려 먹는 거야?
Are you eating tomatoes with salt?

응, 이렇게 하면 토마토가 좀 더 달게 느껴지거든.
Yes, it makes the tomatoes taste a little sweeter.

토마토에는 무조건 설탕이지! 얼마나 맛있는데.
You should absolutely go with sugar for tomatoes! It’s really delicious.

설탕은 토마토에 있는 비타민 흡수를 방해해서 같이 먹으면 안 돼.
You should not eat it together because sugar interferes with the absorption of vitamins from tomatoes.

음식에도 궁합이 있어서 같이 먹으면 좋은 음식, 나쁜 음식이 있어.
There is also a combination of good food and bad food to eat together.

닭고기하고 인삼은 어때?
How about chicken and ginseng?

닭고기하고 인삼은 정말 좋은 궁합이야. 그건 많이 먹어도 돼.
Chicken and ginseng are a really good combination. You can eat a lot of that.

그럼 나 이따가 삼계탕 먹으러 가는데 우리 같이 갈래?
Then, do you want to go with me? I’m going to eat Samgyetang later.

Related words
느껴지다 to get a feeling
궁합 combination
인삼 ginseng
삼계탕 ginseng chicken soup (A dish made by boiling down a young chicken stuffed with ginseng, sticky rice, jujubes, etc.)

Source: Yonsei University. Korean Language Institute