This is the 13356th most frequent Russian word.
набираться
"Набираться" means "to gain, acquire, or accumulate (experience, strength, courage, etc.)."
In this sentence, 'набираться' is used to describe actively gaining or accumulating something intangible, such as experience.
Я люблю набираться опыта, работая в разных областях.
I love to gain experience by working in different fields.
Here, 'набираться' refers to the gradual accumulation of a state or condition, in this case, fatigue.
Туристы нередко набираются усталости, гуляя по многим достопримечательностям за день.
Tourists often accumulate fatigue by visiting many attractions in a day.
In this example, 'набираться' is used in the context of recovering or gathering a resource, specifically strength.