I went to London once for about a week with a friend a few years ago so I’ll weigh in a bit. First do NOT go the London Science Museum It’s full of replicas and fake models of scientific items and barely had any interactive displays. Every time I thought I was looking at a real piece of science history, it turned out to be a fake copy and it was extremely disappointing overall.
Next door however is the Natural History Museum. That museum was great and I definitely recommend it! It had great displays, the building was huge, and had a bunch of things to see and learn about. I think it was my favorite museum to visit though the British Musuem was another with a lot to see and a really good museum to explore! The British Museum has a bunch of real historical items, someone could spend a full day there if they wanted to. Both these museums are worth a visit and I think these two museums are free admission (though you may need to book online nowadays, though not sure).
The Tower of London was really interesting to see too! Cool architecture and an interesting tour. They also have ravens raised there that you can go really close to. I took a ‘selfie’ photo next to one and was only a foot away from it.
Piccadilly Circus is like going into Times Square in New York City. If you want to look at older architecture and historic areas, I do not recommend going into this area.
You may want to go on a “ghost tour” in London. You can look them up and some are free while others may cost something. They’re interesting because you meet a tour guide/group in a historical part of London usually in early evening and walk around different areas while learning about history like the plague, historical figures like Guy Fawkes, and also learn about catacombs and other areas with a lot of history and possible hauntings. (My tour guide showed us a stone building with divots in its walls and informed us it was a result from shells in WW2.)
For food I recommend getting ice cream at least once from a street stand! They put Cadbury flakes (a stick of chocolate) in your ice cream cone and it’s delicious! My friend and I also enjoyed fish and chips and shrimp scampi from local restaurants.
Hope you enjoy your trip!!!