Plattsburgh is a city of 20,000 located on the north-western shore of Lake Champlain. It lies just outside the boundaries of Adirondack Park. There are some nice options for running in Plattsburgh, with several central routes that can be combined in various ways.
For some nice running along Lake Champlain, there’s the Terry Gordon Bike Path, with an optional extension to Peace Point Park. There’s also a nice trail along the Saranac River. For a longer run in that area, combine with the pleasant paths around SUNY Plattsburgh, which also features a running track and several miles of trails in Rugar Woods (a popular spot for cross-country running meets). Another great place to run in Plattsburgh is Point Au Roche State Park, where there are the 15+ miles of trails over open & wooded terrain, with some lovely water & marsh sections. Note there’s as ferry to Grand Isle from Cumberland Head, where you can enjoy some wonderful running on the Lake Champlain Islands.
Note: Plattsburgh winters are very cold & snowy. Paths and trails might not be maintained.