Learn Hardcore Korean: yeoreumeneun badasga-eseo suyeonghagi johayo. - In summer, it’s nice to swim at the beach.

여름에는 literally means “as for summer” or “in summer.” The particle -에 marks a point in time (“in summer”), while -에는 adds the topic nuance (“when it comes to summer, …”). Using -에는 often implies a contrast with other seasons or times (e.g. in spring, autumn, winter it might be different).

Why do we say 바닷가에서 instead of 바닷가에?

The particle -에서 indicates the location where an action takes place (“at the beach”). In contrast, -에 simply marks a destination or existence (“to the beach” or “at the beach” in the sense of “be at”). Since 수영하기 (swimming) is an action, you need 바닷가에서 to show “swimming at the beach.”

Why is it 수영하기 and not 수영하다 or 수영해요?

To express that “swimming is good” or “it’s good to swim,” Korean uses the nominalized verb form verb stem + -기. So:

수영하다 → 수영하 + 기 → 수영하기
Then you attach 좋다 (“to be good”) to say that the activity itself is good. If you said 수영하다 좋아요, it would be ungrammatical, and 수영해요 would mean “I swim” rather than “it’s good to swim.”

How does the structure [verb stem] + -기 + 좋다 work in general?

Start with a verb, e.g. 먹다 (to eat).
Drop -다 to get the stem: 먹.
Add -기: 먹기. This turns the verb into a noun-like concept “eating.”
Add 좋다: 먹기 좋아요 = “It’s good to eat” or “It’s good for eating.”

This pattern expresses that the action is favorable or easy in a certain context.

Why is 좋다 used here instead of 좋아하다?

좋다 is an adjective meaning “to be good” or “to be nice.” It describes the general quality of the situation (“Swimming at the beach in summer is good”).
좋아하다 is a verb meaning “to like (something).” If you said 수영하기를 좋아해요, you would be saying “I like swimming,” focusing on your personal preference, not on whether the activity is generally good in that context.

Could we say 바다에서 instead of 바닷가에서?

Yes, 바다에서 수영하기 좋아요 is grammatically fine and means “It’s good to swim in the sea.” However, 바닷가 (“beach or seaside area”) is more natural when you picture swimming near the shore; 바다 (“sea”) can imply swimming out in open water.

Why can’t we use 수영하러 in this sentence, like 수영하러 좋아요?

-하러 attaches to a verb stem to show purpose and must be followed by a directional action verb (가다, 오다, etc.), e.g. 수영하러 바닷가에 가요 (“I go to the beach to swim”). You can’t attach -하러 directly to 좋다, because 좋다 isn’t a motion verb and -하러 doesn’t create a noun form the way -기 does.