Access to the mount is either on foot across the causeway (about a mile), or by one of the free Passeur shuttle buses which run frequently from 07:30 to 12:00. Attempting to reach Mont Saint-Michel by any other route than the causeway/bridge can be dangerous.
Due to the tourist nature of the mount it can get very busy, especially in high summer. Because of the steep steps up to the abbey, people can sometimes feel unwell, and may want to rest in the numerous gardens throughout the mount with plenty of seats. Keep walking when others are behind you as causing a blockage is likely to annoy them.
Sunday is a good day to avoid visiting the mount as it tends to be the most popular day of the week. It is also best to avoid the middle of the day as coach tours arrive around 10:30 and leave around 16:00, so visiting outside of these hours is advisable to miss the largest crowds.