Senasqua park in Croton, also on the Hudson, is lovely.
Brighton Brook Sanctuary in Croton has nice trails through lovely woods.
The Croton Arboretum has nice paths through woods and wetlands (
Croton Arboretum) and connects to the village trails which lead up into the highlands and have great views.
The Croton Aqueduct trail is gorgeous.
The bridge over the croton dam is stunning:
Northern Westchester Home: Zen Spot
The blue mountain reservation has great trails, many with wonderful vistas:
Northern Westchester Home: Blue Mountain Reservation
And 10 minutes inland, Turkey Mountain is great:
Northern Westchester Home: Turkey Mountain Nature Preserve
Have fun!