The farther east you travel along the North Shore, the more rural it gets. Around Oyster Bay [1], the traffic thins out considerably, and by the time you reach Centerport—located less than 20 miles from the Queens-Nassau border—you’ve left the city far behind.
Route 25A, also known as Northern Boulevard and North Hempstead Turnpike in Nassau County, is the northernmost major route that traverses Long Island [2], and the best one to use for unhurried exploring.
Running parallel to it to the south is the Long Island Expressway (LIE), or I-495, which is the quicker route (except during rush hour) and therefore good to use when driving directly to a specific site.
Links:
[1] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/oyster-bay
[2] http://www.moon.com/destinations/new-york-city-long-island/long-island
[3] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/great-neck-and-port-washington-peninsulas
[4] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/old-westbury-gardens
[5] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/sagamore-hill
[6] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/cold-spring-harbor
[7] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/old-bethpage-village
[8] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/stony-brook
[9] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/port-jefferson
[10] http://www.moon.com/destinations/new-york-city-long-island/long-island/the-north-shore/riverhead