A fabulous run with water and skyline views. It’s ~4 miles around the perimeter, on a dedicated path nearly the whole way. There are parks on each end of the island, which have some of their own paths. The guide below has more details on access and running/walking options.

Access: Via subway. Also a tram from Manhattan. From Queens, access by foot you by crossing the Queensboro Bridge over the island to Queens and then doubling back — about 1.6 miles. More direct access is via tram or subway. 

Add-Ons: Extra paths in the interior parks on the island.

Roosevelt Island Access and Information   Tram Info