RESTful API design - naming an "activity" resource

When designing the endpoints for an activity resource that provides information on the activity of other resources such as users and organisations we are struggling with naming conventions.

What would be more semantic:

/organisations/activity
/organisations/activity/${activityId}
/users/activity
/users/activity/${activityId}

OR

/activity/users/${activityId}
/activity/users
/activity/organisations/${activityId}
/activity/organisations

via AndrewMcLagan