From my office: the Landguard Fort, partly dating back to 1540, the only UK fortification to have been called upon to repel a Dutch invasion on the land, and later rebuilt for the Napoleonic wars, WW1 and WW2. We have long memories on this part of the coast, and keep it good and ready in case the Dutch or French get uppity again.

From home: the Control Tower of Martlesham Heath aerodrome, Royal Flying Corps field pre-1914, later RAF (WW1) & USAF (WW2).