Not all those who wander are lost, but I certainly am!
If you want to see London from great heights there are a couple of options available to you. You can climb the memorial for the Great Fire of London, there’s the top of St. Paul’s Basilica, and the top of the Shard. The most popular option however and the most well known is the London Eye.
No doubt you’ve seen pictures of it before, or at the very least heard of it. It’s a giant ferris wheel on the banks of the river Thames, with capsules instead of seats. It rotates slowly enough that it’s easy to get on while it’s still moving and you get excellent views of the city all the way up and back down again, not just at the top. I’ve only been once, near sunset, but I would be willing to bet the view at night is spectacular. On my way up to the Scottish Highlands I flew over London, all lit up.

You can get there very easily by taking the tube to Westminster on the Circle, District, and Jubilee lines. Just a short walk across a bridge and you’re there! Alternatively you could walk there from the Waterloo Station, but personally I find the better view comes from crossing the bridge.
Book ahead, it costs roughly £25 if you book ahead, £31 if you get there on the day and wait in line. You can also get tickets which give you access to other attractions in London like the river cruises or Madam Tussades.

Bring a camera, you’ll want to capture the views, and a pair of good walking shoes because as much as the London Eye is worth seeing, you can’t really spend the entire day there. The entire ride takes about half an hour, and the lineup might take that or a bit longer. If you want to spend the day in the area I recommend seeing Westminster Abbey, Big Ben, the Parliament Building, Buckingham Palace, Trafalgar Square, the National Museum, and 10 Downing Street. They’re all within walking distance!
Wash your hands, wear a mask, stay home, and stay safe gentle reader.