Then here is the tip: Take the uptown A-train and go almost to the end. At the Northern end of Manhattan you find Fort Tyron Park, a little mountain with a Cloister on top from which you have spectacular views over the Hudson.
The Cloister is a museum operated by the Met that exhibits an extensive collection of medieval art and architecture, including the buildings themselves, which stem from five different Abbeys in Europe and have been deconstructed and transported to be rebuilt in Fort Tyron Park.
Equally impressive as the Cloister are the gardens in front, especially in Spring time. There are many steps up and down, bridges and tunnels, as there should be in an enchanted cloister garden.
You can extend your walk northwards to Inwood Hill Park, or southwards along the Hudson.
Enjoy your day!