...of the Great Conservatory. According to the blue plaque inside, it was...
"Built between 1820 and 1827 by the 3rd Duke of Northumberland to a design by Charles Fowler,
whose work includes Covent Garden market. One of England's first great conservatories,
the building was studied by Joseph Paxton for his design of the Crystal Palace.
It was restored in 1987 by the 10th Duke of Northumberland."

Sadly, the view is somewhat scarred
by the GlaxoSmithKlineThomasBeecham building,
rearing its ugly head behind it, on the left....

(Best viewed at 'original' size!)