Ausable Chasm.

US 9 just north of the Keene exit, between the Adirondacks and Lake Champlain. Ausable Chasm has been operating as a paid attraction since 1870, which puts it in the running for the oldest tourist destination in New York State. The geology is the actual draw: a Potsdam sandstone gorge cut by the Ausable River, with cliffs that run 50 to 200 feet deep and a series of narrow flumes downstream. The basic ticket buys you the rim trails and the walkway down through the gorge, which is a self-paced loop that takes 90 minutes to two hours. The upcharges are where the experience scales: tubing and rafting the river below the walkway, classic and lantern tours, and a via ferrata-style climb for adults who want a vertical day. Hours and admission run on a published seasonal schedule on the site; the gorge floor closes earlier in shoulder months for water conditions. Open mid-May through Columbus Day in normal years. Best paired with a Champlain ferry crossing or a Keene Valley hiking morning. Not a half-day visit if you're doing the river add-ons; budget five hours.