That depends on where you are travelling from.
There are no rides at the London Dungeon.
No
no
Yes
Liverpool Street.
Euston
No.
Yes, American citizens do not need a visa to travel to London for short visits, typically up to 6 months.
To enter the United Kingdom, you will need a passport and, from many countries, a visa. Once you are in the United Kingdom, you can go to London freely: there are no internal checkpoints.
You do not need a transit visa, if you do not go out of the airport to see London or change airports at London.
It depends which country you are from, you do not need one for the games themselves but you may need one to enter the country.
London is an expensive city to visit as a tourist so you need to be quite well off to be able to make the most of your stay.