This is the 5163rd most frequent Korean word.
높았고
"높았고" means "was high and" or "was tall and" (past tense, combining "높다" - to be high/tall, and the conjunction "-고").
In this sentence, "높았고" is used to describe a building's height as exceptionally tall.
그 빌딩은 매우 높았고 주변에서 가장 눈에 띄었습니다.
The building was very tall and stood out the most in the area.
Here, "높았고" refers to high temperatures, indicating that the weather was hot.
기온이 높았고 한낮에는 매우 더웠습니다.
The temperature was high, and it was very hot in the midday.
In this example, "높았고" is used figuratively to denote high academic scores of students.