... sounds like a real dull thing to be going to. But quite to the contrary. I normally go twice a year. Somehow I just like going there and looking at plants. I know it sounds boring as hell.
But you can also go there and look at structures, at geometrical forms. You can ask plenty of great "why" questions or just marvle at the incredible amount of details.
Taking photos of plants can be real fun. Trying to bring out some special detail I saw is not always easy but a nice challenge during photography.