I often go over the bridge for a walk, I live on the south bank. You could walk over the bridge and back. I walked from the centre of Hull along the foreshore to Paul, and Heddon and got a bus back.
There is the Country Park close to the bridge. Or walk from the bridge the other way along the river bank. You could get a bus to North Ferriby, or Swanland, or Welton, or Melton, or Elloughton, or South Cave. Lots of nice places to walk in those areas. Good luck.
ilona