I read that these woods have existed for 8,000 years. They are one of few remaining areas of ancient deciduous forest in this part of the city. But like I said, I'm really grateful that any areas of woods still exist at all. It reminds me of Virginia, where we could walk to the end of our street and be in the woods.
In the case of Severndroog Castle, it was built as a memorial to the husband of Lady James of Eltham, in 1783. It did seem to serve some practical purpose because it sits atop a hill and from it's rooftop you can see for miles around Greenwich and Southeast London.