Participants, often in vulnerable states, have little recourse if mistreated or injured.

© Marian Carrasquero for The New York Times

The transportation secretary’s six-part YouTube series is fueling ethical concerns over family adventures funded in large part by corporate sponsors regulated by his department.

© Kenny Holston/The New York Times

Werner Kalecinski is a social media sensation among young Germans. How did he go from heartbroken widower to partying on a yacht?

© Lena Mucha for The New York Times