Chamonix transforms during UTMB week, with its population swelling from 10,000 to 100,000. Runners and fans flock to the area, creating a vibrant, charged environment.

The UTMB race course spans France, Italy, and Switzerland, offering stunning views and challenging terrain. Spectators can catch glimpses of the race at various points along the route. Read more gear coverage.

Security measures have been enhanced to protect runners and the environment, especially at popular viewing spots like Notre Dame de la Gorge, where incidents have occurred in the past. Related: Canadian Ultrarunners Set to Compete at UTMB.

This original Runner World brief is based on reporting from Canadian Running. Visit the source for its complete reporting, context and any later corrections.