This is the 983rd most frequent Serbian word.
планинским
"Планинским" means "mountain" or "mountainous" in English, relating to or characteristic of mountains.
The word "планинским" here describes the paths ("стазама") as being related to the mountains ("планине"). It uses the instrumental plural form to indicate the trails in the mountains.
Волим шетње по планинским стазама.
I love walks along mountain paths.
The word "планинским" modifies "спасавањем" (rescue), denoting the type of rescue as related to mountains. It uses the instrumental singular form.
Бавио се планинским спасавањем током година.
He was involved in mountain rescue over the years.
The word "планинским" here clarifies which regions ("пределима") are being described, specifically those pertaining to the mountains. It uses the dative plural form to describe areas associated with mountains.