10 things to observe while walking
The easiest thing to notice at all given times is your own breath, just follow the rhythm of the in-breath and out breath as you walk.
The sole of your feet
It is more effective when you are walking with bare foot, with shoes on you won't feel a lot of the things under your feet besides a few stones and rough roads here and there (shoes were made for that)
The motion of your hands
This particular sensation can be observed around your shoulders and you can feel the rotating shoulder cap. Don't stop your hand movement when you are conscious about this one.
The movement of your knees
This is one is evident as you take each and every single step, you'll notice your knee cap move and you can't stop this one even when you are conscious about it.
The temperature(hot/cold) around your feet
Temperature as we know is sensed everywhere around the body, but when you put conscious effort to the sole of your feet it becomes very obvious that it is either hot or cold.
The pull of gravity on your palms as you wave your hand.
Oh, it is a nifty one, you will have to carefully take notice as you wave your hands while moving. The area of concentration will be your palms and if you are lucky you will even feel a little blood flow react to gravity as your hands go up and down.
The shockwaves that go to your body, noticeable specially when you walk slowly
As said, works only when walking slow. Walking slow will allow you to notice the little shock wave that comes in when the heel of your foot touches the ground. Walking slowly might even expose you to other small things.
Ambient sounds like the sound of fan or the air flowing
Sounds are always noticeable, but when you walk slow or fast depending on your speed the sounds you hear will be different, you might have experience that when sitting inside a fast moving car or a train. The sounds are more elongated when you go faster.
Recognition of space constraints, specially when moving through small lanes vs big roads
Evident mostly if you are walking indoors and you go from a passage way to a big lawn area, it is mostly because of the air pressure that develops in these areas but a fun thing to notice.
The difference it makes in all the above 9 things, when you change your pace.
Your walking speed will make a huge difference to all the points discussed above, slowing down yourself will give you different results than dashing your way through. Sounds will be specially fun when you dash through places.