Walking
Walking in London is fine. Take some precautions and it’s safe. Get comfy shoes and an umbrella or light waterproofs.
There are no big hills to climb and no major difficulties, in the centre at least.
The roads do not form a grid pattern, and that can be confusing. Crossing the road can be tricky at first. Just look for the crossings and you will be fine.
You can, possibly, walk everywhere in the centre, but it would be slow, hard work. Remember, it’ll be busy.
It’s best, in our opinion, to get public transport to an area and then walk round to see what you can see.