This is the 18764th most frequent Korean word.
실내에는
"Inside the room/building."
In this sentence, 실내에는 is used as the subject of the sentence and indicates the location being talked about, 'indoors.'
실내에는 따뜻한 공기가 가득 차 있습니다.
The indoor area is filled with warm air.
Here, 실내에는 specifies the location within an indoor setting where the tables are being described.
실내에는 꽃으로 장식한 테이블이 있습니다.
Inside, there are tables decorated with flowers.
In this sentence, 실내에는 sets the context by focusing on the indoor environment being quiet.