Pretty central to any London trip, it is hard to stray far from the river. A fair few bars, cafes and restaurants (though never enough!) and great views and lots of people keep the walk interesting and well-oiled enough, wherever you are going!
The Thames is even beach-like in places (I never knew this!), so you can walk 'in the Thames' (beachy enough to walk, you'd be brave to sunbathe or take a dip!).
You can also - as we did - view the South Bank from a Thames Clipper, which I'd recommend too.