This sundial is of a type called an analemmic sundial. Most sundials have a part called a gnomon that casts a shadow upon a dial, where the time is read where the shadow falls. In this sundial, you are the gnomon! You are most welcome to come catch the time anytime the sun is shining. If you want to make a sundial yourself, you can find many resources to help you in the references I link here.
Seasonal Markers for Analemmatic Sundials, Roger Bailey, The Compendium – Journal of the North American Sundial Society, Sep 2003, 10(3):1-7.
A Sundial To Enjoy, Mac Oglesby, The Compendium – Journal of the North American Sundial Society, Sep 1995, 2(3):24-26.