This is the 906th most frequent Korean word.
안전한
"Safe."
Here, '안전한' is used as an adjective describing the safety of the park as a characteristic.
이 공원은 밤에도 매우 안전한 곳입니다.
This park is a very safe place even at night.
In this context, '안전한' is qualifying '여행' (trip) to emphasize the need for it to be secure.
안전한 여행을 위해 준비를 철저히 해야 합니다.
You should prepare thoroughly for a safe trip.
'안전한' is used here to describe the type of environment schools should offer, focusing on it being secure and without threats to safety.