Rowntree Park is always lovely but particularly so in Autumn and just fabulous right now! In Spring it has daffodils and ducklings; there is a ‘reading-café’ which is accessible, a children’s play area and tennis club and you can access the river walkways with their viewing points and the Millennium footbridge over the River Ouse. Parking is reached via Terry Avenue.
The paths are smooth so the whole place is eminently scootable as are the paths by the river. Look out for the flood levels on the dove cote (itself a memorial to Rowntree’s workers who died in WW1) – the one from 2000 is way above your head!
The drawback is that the park does flood so is sometimes closed while levels recede and the place dries out a bit. Also the large amount of geese (or rather their droppings) do mean you can’t just sit anywhere on the grass but there are plenty of benches.
For more information see the council’s page on the park: https://www.york.gov.uk/directory_record/376/rowntree_park and DisabledGo has their usual rather unuser-friendly entry on the café: http://www.disabledgo.com/access-guide/city-of-york-council/rowntree-park-reading-cafe-2