Today I walked along Old Croton Aqueduct trail from Quaker Bridge Road to the New Croton Dam . This is about a mile each way. There are only 3 or 4 parking spots where the trail crosses Quaker Bridge Road and they are sometimes full but I was the only car at 5pm. The trail is on the side of a wooded hill and is shady most of the way except where it goes under some high tension lines about half way to the dam. Summer is coming to an end but the trees were still green.
You used to be able to drive across the dam but the road was closed before 911 to repair a bridge over the spillway at the far end of the dam and will not be reopened because of security concerns. Even when it was open the road didn't get a lot of auto traffic. You can still walk or bicycle across the top.