For girls in the Amazonian Tikuna tribe, their first menstrual period signals not only an important physical change, but a spiritual one, as well. In what is known as the Yüüechíga or pelazón ceremony, girls are isolated from men and their communities after their first periods. The girls spend between three months and one year living alone, either in small dwellings or private rooms in their family homes."For the Tikuna, taking part in this ritual means the transition from being a girl to being accepted as a woman," Lena Mucha , a German photographer who documented the ritual, told Refinery29. "Some of the girls told me that at first, they were afraid, but then really enjoyed that time. It was a moment in their life when they could concentrate on themselves and learn a lot about their traditions and cultural heritage."During the time of the pelazón, girls learn the tribe's music, dances, history, and beliefs from other female tribe members. They let their hair grow long. The ritual is seen as a bridge between childhood and adulthood in the tribe, which lives in the part of the Colombian Amazon near the Brazilian and Peruvian borders."The time of isolation ends with a three-day ceremony where the girls are celebrated. As a symbol of initiation and purification, they get their hair cut...After that ceremony, the girls are back in the daily life of their community, now accepted in their roles as women," Mucha said.Many cultures around the world have traditions and rituals around a girl's first menstruation, but some can leave girls and women feeling shunned. A tradition in Nepal called chaupadi dictates that girls and women must stay outdoors while they have their periods. In other communities, a lack of understanding about what is happening to girls' bodies can make them feel afraid.But Mucha, whose work focused on "the impacts of globalization and modernity on young women coming of age," said the women she spoke with who had gone through pelazón saw it as a positive time. Ahead, she shares these young Tikuna women's stories with Refinery29.Editor's note: All of the captions were provided by Mucha and have been edited for clarity.