OCA actually is well beyond croton-on-Hudson . It is a linear state park 20+ miles that runs south(Bronx border) to north (Putnam border) in westchester . Very diverse - woods, backyards of modest homes and cutting through huge estates (eg Lyndhurst). Some of OCA winds through village streets. It's signature are the column vents that pop up every mile or so to allow flow of water from Catskills (?) to NYC many years ago. Great views of Hudson.
The aquaduct is great and a sight to enjoy. I have lived in NY for so many years and didn't realize such a beautiful place is so near by. It is very calming to watch the aquaduct. Hiking / trekking is quite easy and simple. A nice, quick get-away place.
I started the trail in Tarrytown. It stunk at first because you're cutting through streets and backyard. Once you're in Sleepy Hallow you'll go to a beautiful part of the trail. You'll be along highways for a bit until you hit Ossining and from there's its quiet and peaceful. Just you and the birds!
Pleasant trail for stretching the legs out after a long winter - wide, well-maintained, and not too much up & down for out-of-practice legs to deal with. The trail is accessible from mass transit (I took the Hudson Line to Ossining and followed the trail from there to Tarrytown, about a third of the overall length of the trail. The downside is that the trail spends a lot of time just behind back yards, and is never very far from the road - or out of earshot of cars.