From the water, Great Sacandaga looks endless. From Hadley Mountain it looks like what it is: a long reservoir poured into a valley, with the Conklingville Dam pinching the north end.
The trail is about 3.3 miles round trip, red markers, bedrock underfoot, roughly 1,500 feet of gain. The 1916 fire tower is the postcard; you can see the lake without climbing the stairs. Parking is on Tower Road. In summer a steward is often on the summit. In ice, the rock is the problem, not the distance.
Pair it with the dam
If you have a second hour, the Conklingville Dam viewpoint is the other half of the story — the 1930 earth fill that made the lake, still run by the Hudson River–Black River Regulating District. Flood control first. The beach you stood on in July is not the beach in October because of this structure.
The Town of Day public launch is the north-end put-in if you want the water after the hill.
A summit clip or a dam overview belongs on these listings as soon as you have a file or a YouTube URL. Until then, the trail is the media.