The Imperial Palace is home to the Emperor of Japan and the royal family.
It’s called the ‘皇居’/’koukyo’ which just means ‘imperial residence’
It’s surrounded by moats and security but two days a year it’s open and you can see the royal family from their balcony:
2nd of January for new year and December 23rd for the Emperor’s birthday.
It was actually destroyed in world war two and then reconstructed, like many of Japan’s famous buildings.
It’s in a very central location; only a short walk from Tokyo station.
It’s also a really popular running course, as the outside of the palace makes a clean 5km loop.