The Tower Bridge, the Tower of London and the British Museum.
The Tower of London is another must-see place with the 44 billion dollar collection of the Crown-of-Jewels, and lots of historical exhibitions that includes massive collection of old weaponary and armour. I had bought the tickets on-line, and again the on-line ticket holders were the first to enter when it opened.
After the Tower of London, we did a stroll across the Tower Bridge going via the overhead walkway, then down into the original engine room used to raise the bridge.
The British Museum has an amazing collection of artifacts from around the world that was assembled in the days when assembling such collections was possible! It wasn't very easy getting a photo of the Rosetta Stone. It had a prominent display location, and every person going past wanted a selfie next to it.