You can use an assignment to require the students to tell you that they have completed an activity outside of Moodle. For example, you can instruct your Art students to build an outdoor sculpture. Then, their submission will consist of notifying you, It's built and ready for you to review.
Even when you don't require students to upload or submit anything, you can give a grade for the assignment. This is a good way to get work done outside of class, into the grade book. In the following screenshot, you see an assignment that the student will do offline:
