Northern Westchester looks nothing like the city an hour to the south. Around North Castle and its main village, Armonk, the land is a quilt of rocky hills, old stone walls, big wooded properties and reservoirs, with narrow roads winding between them. Corporate campuses hide in the trees, among them the headquarters of IBM, which has been based in Armonk for decades, but from the saddle you mostly see woods, horse farms and water.
History lies thick on this ground. In the autumn of 1776, after the Battle of White Plains, George Washington pulled his army back into these hills, and a farmhouse in the North Castle area served as his headquarters. Later in the war, it was at North Castle that the captured British spy Major John André was first held before being taken away for trial. The stone walls you see running through the woods were built by farmers who cleared the land, long before the forests grew back.
About the swim, honesty is in order. The large lakes you see here, including the Kensico and Byram Lake reservoirs, are part of the water supply for New York City and nearby towns, and swimming in them is strictly forbidden, with police patrols and fines. Many of the local beaches and pools are reserved for residents. If you want water, the public beaches of Long Island Sound to the east, around Rye, or the larger state parks farther north are the realistic options, so plan the cool-off accordingly, or settle for a splash at a stream.
The riding is lovely and fiddly. Roads such as Route 22, Route 128 and the smaller lanes between Armonk, Bedford and Pound Ridge twist through the trees, over short rises and around blind corners, with stone walls right at the edge of the tarmac. Surfaces vary, potholes appear after winter, and you will share the road with commuters, cyclists and horse trailers. Autumn is spectacular, when the maples and oaks turn red and gold and the light comes low through the trees.
Armonk has fuel, delis, coffee and restaurants, and Chappaqua and Mount Kisco nearby have more. From here the way back to the city runs down the parkways, where traffic builds quickly on weekend evenings, so a late afternoon start home is wise if you want to avoid the crush.