The City Green is a public park in Marcuria. In the middle stands the tree-shaped house of Abnaxus, Venar ambassador to the High Council of Ayrede. There is also a flowerbed where April may plant the Organic Plastic Leaf to open the Book of Secrets.
There is a large plant in the foreground, and April wonders whether it might be carnivorous. She comments that "It's Audrey's long-lost cousin", after Audrey Junior the carnivorous talking plant in Little Shop of Horrors (1960).
Concept art features the caption "Find the apple", which may imply that a puzzle involving an apple was once involved in the location. Perhaps this was originally how the Book of Secrets was opened.
Okay, I found it. Now what? © Funcom