You didnt mention what part of the country..... Just excellent ones at Desert Gardens Oasis RV park in Florence, Az. Lots of them and VERY smooth! They groom them every week and its miles through the desert with the saguaro's. southwestjudy
My favorite has been the carriage roads at Acadia National Park in Maine....I don't recall how close the trails were to the campgrounds. Obviously, these would be better enjoyed during the summer months.
I also enjoyed riding my bike at the beach during low tide at Anastasia State Park in St. Augustine, FL.