It's what's left of Whitehall Palace. Designed by Inigo Jones. The story of the unification of England and Scotland by James I. His son's homage to him included the Reubens paintings on the ceiling. Then the final insult, Charles I's execution in this very location. It is not a showy place from outside but the art is amazing. I recommend you use the audio guide for the full story. Included in the London Pass.
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