Your profile photo, name, and location are visible to everyone. This enables other members to confirm that they've found the person they were looking to connect with.
Your reviews and uploaded trail photos are also public, as the intention is to help other AllTrails members gain trail insights ahead of their adventures.
You can control who, if anyone, is able to view your community (Followers/Following lists), completed trails, activities, maps, and lists. You can learn how to adjust your default settings for the above items by reading this article.
Note: You also have the ability to adjust the privacy settings for an individual activity, map, or list, without updating your default privacy settings. These articles explain how to adjust the privacy settings for each type of content: