Actually, If you are staying at the Hilton, you will be right across the street form Point State Park. It attaches directly to the Riverfront and North shore trails, both of which are easy and flat. Just have to watch for pedestrian traffic.
It is also very easy to get to the Eliza furnace and south side trails from there. It would take about half a mile of easy city street riding but those are also nice and flat and scenic.
You can check out the map online off the main page for more specifics.