The "regular" activity page (https://stackoverflow.com/users/[user_id_here]?tab=activity) is accessible by clicking the Activity tab on one's profile page. When there is activity on one's questions or favorites, etc., the browser shows a banner across the top saying, for example, "You have 1 new response." Clicking that banner opens the "other" activity page, entitled Recent Activity (https://stackoverflow.com/users/recent/[user_id_here]/?tab=responses), which presents similar but different details.
I find this other activity page much more useful for some things. For example, it makes it easier than the reputation graph to see exactly what has bumped up my reputation. Also, it categorizes activity by tabs, which is quite helpful.
Now that I have bookmarked this Recent Activity page I have it readily available, but I am just wondering why it is somewhat hidden (i.e. does not have a link on the profile page) ?