The Saratoga Battlefield is a must, a great and safe ride on a one way road with a bike lane for a good bit of it About 11 miles if you go around all the side loops. Tons and tons of history. The bike clubs do evening rides during the week on various days.
Zim Smith trail has just been extended three more miles right into Mechanicville. The new section is non rail-trail, which means it has some hills, swoops and turns and is very lovely and far more interesting than the northern end. The Champlain path is being extended northwards into Mechanicville and when that section opens you’ll be able to go from Ballston Spa village all the way into Waterford and then on to Albany, though Watervliet will still be on (safe) streets.
The Warren County Bikeway from Hudson Falls through Glens Falls to Lake George is another winner. Again, not a rail trail, all paved, but with some decent hills and beautiful riding through a forest as you get closer to Lake George. It pops out of the woods right at the million dollar beach.
Right across the Hudson into Washington County are tons of wonderful gravel roads going through farm country all over the place. Schuylerville out to and around Lake Cossayuna and back is a nice trip, many ways to do it. Mosquito Swamp Road (no kidding) is a great dirt road, pure joy on a gravel style bike.
Saratoga Lake itself is a very pretty ride, other than all those people trying to kill you the whole way. Very little or no shoulder and too many people not paying attention especially on the weekend in the summer, but it certainly ain’t boring!