Woolwich Ferry
Woolwich straddles the river in the east. If you are going there, and it’s unlikely you will be, there’s a DLR train to King George V on the north side, and Woolwich (Elizabeth line) and Woolwich Arsenal (DLR, trains from London Bridge etc) in the south.
Woolwich is a grim place, most famous for having the first ever McDonald’s in the UK.
But walk down to the river and you can catch the free ferry from one side to the other. It’s great fun, especially on a sunny day.
Also, walk down to see the Thames Barrier.