While everyone is gawking at the House of Parliament and snapping photos of Big Ben or the gigantic statute of Winston Churchill, turn your back on the 'the Ben' and you will face an inconspicuous building across the street from the park: The British Supreme Court. Other than the inconvenience of a security checkpoint, you will find a delightful little restaurant downstairs while reviewing some major legal landmarks in a small museum. Take the rotund staircase to see, feel, touch any or all 3 courtrooms (when not in session). Friendly and helpful staff!
Just the break you might need after hours of walking.