The inside of the greenhouse will be filled with plants and natural decorations.
The outside will basically be like the real burggarten. Maybe I will give it a little twist.
A shed for tools and stuff. A library, because… it reminds me of Hogwarts, somehow. Dungeons, because DIY dungeons are so hot. Then expand onto the outer decorations, making either a sea, lake or forest.
The most obvious thing you need is plants and other stuff inside your greenhouse.
(And you need names for those locations, to encourage explorers - make tricky map locations!)