A visually impaired Michigan woman, who was on a quest to see the world before she went completely blind, vanished while vacationing in Peru, just a day after she climbed the highest peak of Machu Picchu, her worried family said.
"So it's my belief that she wanted to see and experience as much as she could before she couldn't see anymore. I think that is a driving force for her. She wanted to travel as much as she could whether with friends or independently."
He said his father, Carlos Valpeoz Sr., traveled to Peru to help police search for her.
Carla Valpeoz, who walked with a white cane, went to Peru the first week of this month for a friend's wedding, her brother said. She decided to travel around the South American country alone and celebrated her 35th birthday there on Dec. 8, he said.
He said his sister took an airplane to Cusco in the Peruvian Andes and set off on her own on Dec. 11 to visit the ancient Inca ruins of Machu Picchu.
But when she arrived at the ruins, employees there discouraged her from going on by herself due to her disability and the rugged terrain, her brother said.
He said a tour group overheard her speaking with the workers and invited her to join them.
"They helped her and spent the entire day with her in Machu Picchu. And there are photos that show her at like the highest peak over there," Carlos Valpeoz told ABC News.
He said his sister and the members of the tour group, which included Spanish and Argentinian tourists, went back to Cusco together and celebrated at a club in the city.
"They were extremely excited about their adventure," said the brother, who has spoken on the phone with members of the tour group. "They conquered Machu Picchu and they wanted to go celebrate."
He said his sister shared a room with a woman at the Pariwana Hostel in Cusco.
He said the roommate awoke about 9:30 a.m. on Wednesday, but Carla Valpeoz had already packed up and was gone.
He said his sister sent a WhatsApp message to an Argentinian man from the tour group at about 10 a.m. on Wednesday, saying she was going off to see some sights and asked if he was interested in going to a museum in Cusco later that day.
That was apparently the last anyone heard from her, he said.
A U.S. State Department official told ABC News that the department is aware of the reports of a U.S. citizen missing in Peru.
"When a U.S. citizen is missing, we work closely with local authorities as they carry out their search efforts."
"The U.S. Department of State and our embassies and consulates abroad have no greater responsibility than the protection of U.S. citizens overseas," the official said. "Due to privacy concerns, we have no further comment."
Police told the Valpeoz family that investigators have obtained security video of her getting into a taxi Wednesday morning and believe she went to a transportation hub in the city to catch a bus or shuttle to go sightseeing.
She was scheduled to meet a friend, Alicia Steel, who is also from Detroit, at the airport in Lima on Saturday and they were to fly back to Michigan together. When Valpeoz failed to show up, Steel reported her missing to police and canceled her own flight home to help in the search for Carla, according to Carlos Valpeoz.
"There's no way that she would worry anyone by not contacting them," he said. "She would have tried to establish some kind of contact with somebody by now."
He said his sister has frequently gone on trips alone, traveling Yemen, Egypt and throughout Central and South America. He said she once taught English in Papua New Guinea.
"She's missed a couple of flights here and there and had to reschedule," her brother explained. "She's gotten turned around a little bit. But the thing that's extremely out of character about this situation is the fact that she has made absolutely no contact with her friends."
Carla Valpeoz is an advocate for the visually-impaired and author of the travel book "Visionless Adventures." She also worked as a tour guide at the Arab American National Museum in the Detroit, Michigan suburb of Dearborn.
In a YouTube video she posted, she said she was diagnosed with optic nerve atrophy when she was 10-years-old and has been gradually going blind ever since.
"My adventurous spirit challenged me to step out of my comfort zone, giving me the opportunity to live among different cultures and communities," she said in the video. "I want to create a platform and I want to bridge communities of cultures and carry out workshops so that we can learn to work together."
ABC News' Conor Finnegan contributed to this report.